RAM Slot Order? RAM upgrade/replacement on older unit)Slot

I'm sorry, I should have noticed with your scan, but the motherboard model you supplied confirms that you have one of the older Socket B motherboards with 6 DIMM slots. Your motherboard socket was discontinued in 2012, and most (if not all) more modern processors don't support 6 DIMMs.

Everything I said is still relevant to almost every non-server/workstation motherboard in recent years, and if you choose to upgrade your motherboard and CPU, that is what you probably will be needing (but again, still make sure your motherboard would support it).

In your case, it is optimal to run in triple channel, so a triple channel kit will yield the best performance, even if it comes with slightly less RAM (like 12gb instead of 16gb). It looks like it also only supports up to 4gb per DIMM, so it looks like you need to go for a 3x4gb triple channel with DDR3 1066 PC3-8500... but this looks like it's really hard to find now a days, and if you do, it could be over-priced. Getting to this point, it's debatable whether simply upgrading your RAM is going to help you much at all.

From the left, it looks like the second, fourth, and sixth DIMM slot are optimal for triple channel operation (1, 3, and 5). You could also use another kit in 2, 4, and 6 for 24gb, but like I mentioned, this might not give you any performance increase depending on load, and is likely not worth the money at the moment, as supply is lower and prices are jacked up. Your oscillating 1gb and 2gb show that your RAM is optimal for your motherboard's optimal triple channel operation.

"Upgrading" with your current components might not be worth a lot. Going from 2 1 2 1 2 1 gb to 0 4 0 4 0 4 gb should be better, but probably wouldn't be worth the money, especially considering what you'd be doing - and if you plan on doing more extensive tasks, upgrading your CPU would be more effective (but that requires a new motherboard).

If you can afford to upgrade your CPU and motherboard, it might be worth it for you this day and age, but it all depends on how often you use your PC, what you use it for, how much it's worth to you, and how much you can afford to spend on it.

It looks like you have an i7 9xx from 2009-2011 - I'm guessing this is suitable for what you're using your computer for? If you find it isn't, like I mentioned in the original reply, waiting for a newer motherboard and processor to upgrade your RAM could end up being very expensive, and potentially not worth it if you absolutely don't need it, want it, or can't afford it.

There are a lot of budget options for upgrading into more modern PC's, even if you don't need the top-of-the-line performance. For any new processor, you're going to need a new motherboard (also are budget options) and if you're really into to being able to upgrade, AMD might be a good thing to go for. I'm a huge Intel fan, but with AMD, they have things like the AM4 socket, which supports a wide range of processors that might be compatible with future releases. With Intel, you're usually limited to a single generation (like with my i7 8700k 8th gen LGA 1151) or even the socket you have now.

So, you could get a triple channel kit with 3x4gb with that motherboard, but it might not even be worth doing, both for price or performance. It might be a little better, but probably not warranting the cost, and getting a new motherboard and CPU would likely yield a better performance per dollar increase.

Sorry for my initial confusion, I hope I have helped and can continue to help in any way I can. Knowing what you want/need/expect is crucial to making your decision.
Not sure how much you know about assembling custom PC's or how much you're willing to learn, but I'd recommend it if you want to get the best value for your money and have the time to spare to do extensive researching (if you don't already know).

Mostly depends on what i7 9xx you actually have and what graphics card you're expecting.
If you really can't/don't want to spend more money and you feel like coasting with new RAM is reasonable for the price, then by all means go for it, but don't expect the RAM upgrade to save your PC if you feel it isn't performing up to snuff.

Pre-builts under/around $500 are a bit iffy, and I wonder if they'd really give significant enough of an improvement to be worth ditching you current hardware. I don't know the exact specs of your processor and newer graphics card or what you do or want from your PC, so I don't know. A lot of them come with only integrated graphics, too. They often add a decent chunk to MSRP for assembly. To get a better PC with your budget, you'd need to go custom, but you might not need to based on your performance preferences. There are a lot of factors at play with this, but there's also the possibility for bottlenecking, but if you don't go overboard with any one component over the other, there shouldn't be problems. This is mostly only relevant when you pair a new top-of-the-line component with an old mediocre one. Generally (for maximum performance at least) you want to upgrade at the same time (even more $ ), but even when I had my old CPU, upgrading just the graphics card was definitely amazing.
I'm big into value per dollar and longevity, but that comes at a significant premium ($1000's, literally )
I believe I've put over 4 times more money into my PC then my car. :lol: This is a personal choice, you have to make your own.

Ultimately, if you're fine with it, stay with it.
Consider what you want from it and what you're willing to pay. If you're not willing to pay much more, then you're generally not going to get much more, but for many people, perhaps you included, you're just fine where you are and I respect that.

Are you monitoring your CPU and GPU temps? Your 950 has a TDP of 130W - this is pretty high, and if it's not properly managed, you could run into issues... otherwise, like I mentioned, your hardware is older, and if it's working it's working, but there's no guarantee how long it'll last (that goes both ways )

If you're keeping it, depending on peripherals, 460W could be okay. If you don't overclock anything with just your CPU and GPU factored in, your load wattage might be around 360W... but if your PSU is really old and might stop working properly it could be cutting it close. Beyond pure wattage, it might not be advisable to keep the same PSU for more than 5 years, unless if specifies a warranty matching or beyond this.

$700-1000 is more around the range I'd personally consider a pre-built worth buying (at least as a solid upgrade from your components). I'd personally consider an upgrade if not just because everything is getting physically old by this point. Your CPU could be close to kicking it, but it could also easy have another five (or more?) years left - it depends on a lot of factors. Even if you're not into really heavy stuff, it could be advisable to change out a build every 5-6 years. It's a lot of money, but it could end up saving you time and making the time you spend more valuable.

Like I mentioned earlier, if you're having to replace each and every piece in your computer bit by bit, eventually you're going to have to (or want to) overhaul the whole thing, and at that point, if you don't like custom assembly, it might be easier to go for a brand new pre-built. I'd recommend looking into the specifications and compare different retailers to get the best price to performance with the least added onto the individual retail price of the components. I didn't build my first custom PC, actually, and it was still a pretty good value. It's a bit of work itself, but I think it's worth it if you're planning on keeping it for years.

It's your life and your money though, you have the last decision. Again, I hope I can help at all...

I'm glad if I could help literally at all
Sorry I'm a bit late back. -~-
Before assembly and final preparation, I'd recommend watching something like "Avoiding Common PC Building Traps" Episodes 1-4 by Techquickie and perhaps other similar videos. They helped me make sure I didn't overlook something "simple".

If you already haven't gone for it, you'd probably be best going for the B450 like profoundnoah and cryoburner suggested over the AB350 for your AM4 socket.

Also note that slow boot times can also signify problems with the HDD (hard-drive), but since your other components may be on the fritz, I'd wait to see how your new build goes (just keep this in mind). If you notice file transfer or boot times very suddenly decreasing significantly, it could signify a failing drive. Don't want to overstimulate you, but I don't want you to lose any of your data.

Regardless of whether the drive is having problems, make sure you have a backup, just in case. If you end up needing to buy new, HDD's will have a bit lesser performance in general, but the alternative SSD's are far too expensive right due to the V-NAND shortage and manufacturing difficulties, and I wouldn't recommend buying one even if you could afford it until late 2018 or early 2019 (maybe). I don't even have one at the moment I'd recommend a 7200rmp HDD, brands are preference, but know that for Western Digital that there's a difference between a WD Blue, Black, Yellow, Red, and Purple.