AMD Phenom II X4 955 B.E to AMD Athlon 860K Worth it?

NO. I have/have had both processors. Actually, it was the 965 BE. The 860K is a sideways move in gaming performance.
My 965 @ 4GHz actually out performed my 860K @ 4.2 Ghz

I might add, your GTX 570 is probably the weak link right now anyway. If you can get the 955 up to 3.6GHz or more, it will keep up with a faster card. My 965 @ 4GHz handles the GTX 960 in my sig below.

What board do you have the PhII in.

Yeah, that's not a board you'd want to OC that 125W processor on anyway. I guess you will have to decide how far you want to go with an upgrade...
Replacing the board with one you can OC the PhII with would probably be the cheapest route for the least return. Moving to a new Intel platform would cost more but provide for a better upgrade path forward. Somewhere in the middle would be to move to a later AMD platform (fx-8350 and 990FX board).

I find it odd that the 955 is constantly at 90% while the GTX 570 is only able to garner 50% usage. Seems to me from my PhII rig that the GTX 570 should not be bottle necked by that Phenom II. Those must be CPU limited games that don't require much GPU usage, and not really a bottle neck situation.

If you aren't willing to upgrade the GPU, there's no sense moving to an Intel platform. The GTX 570 is down there with today's entry level/mid level cards: http://www.tomshardware.com/reviews/gpu-hierarchy,4388.html
Since you feel your board is failing, it might be better to simply replace it with a new board that is able to safely be OC'ed. Then OC the PhII a bit.
But keep in mind, changing motherboards might require a clean install of Win. Even if the system boots up with the new board, you'll want to do some major housekeeping to get the Registry cleaned up.

Intel
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This CPU: http://www.newegg.com/Product/Product.aspx?Item=N82E16819117561
One of these boards depending on your needs: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&N=100007627%20600567584%20600567581
One of these gfx cards: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&N=100007709%20600536049%20600536050%20600537575%20600565061%20601107976
Note: If you get a board that requires DDR4 RAM, you'll have to buy that too.

AMD
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One of these boards: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&IsNodeId=1&N=100007625%20600138080%20600166242%204814
They will accept your PhII for now and have an upgrade path for a faster processor in the future.

The difference will mainly be centered around the gfx card upgrade. But the Intel CPU will be able to keep up with massively faster gfx cards than the PhII.
If you don't care about OC'ing the CPU, you can get the i5-6600 (non-K) and a cheaper board: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007627%20600567584&IsNodeId=1
You can go to Newegg Canada and compare prices.

Coming from an upgrade of a 550ti to an r7 370, a 570 to 960 will be roughly the same jump/if not a better jump. CS:GO is a fairly CPU intensive game (it ain't that taxing on your gpu, face it. It's running on source.) At the moment, if you're not looking to do a complete overhaul I would (personally) grab a better MB and just OC the PhII. The other option would be to upgrade the MB and the CPU at the same time as suggested above. If you're looking to upgrade through an i5 Intel route or a newer AMD route (for budget I would grab a 990FX board and an FX 6350 at this point), the AMD will be less money, but as said above, will not talk to your GPU as well. Although for your games, I don't know that that will matter. I'm running an FX 6100 OCd to 4.0 GHz air cooled with an R7 370 and running CS:GO at 250 FPS. I do keep everything on low to help focus in the game though. Less eye candy. The fx 6350 is 125 less than a 6600, 160 less than a 6600k.

^ (mostly) agree. I was going to recommand an Antec 900, as that's the case I'm currently running (and now have my CPU OCd to 4.4GHz :'D. However, looking at the specs of that case, IF YOU CAN SUSPEND IT CORRECTLY, that actually has far more air flow. The only thing I don't like about that case in a brief overview is that it's metal/plastic and not pure metal. But honestly that's being knit-picky. If you can find a way to get that sucker mounted to a wall so that you leave the bottom open, it'll be an awesome air cooled case. As for the 8370, I don't know that the extra $40 price tag on it between an 8350 and an 8370 is actually worth an extra .1GHz Turbo. Honestly, I would still look into an 8350 over it.
http://cpuboss.com/cpus/AMD-Phenom-II-X4-955-vs-AMD-FX-6300
That is a test between a 6300 and your current chip. The stocks are not all that different, as you can see. It's not a giant leap forward, and with AMD Zen coming out q4 this year, I would be hesitant to upgrade your cpu with your mobo. Especially if you're looking for a budget buy. I went with the 6300 test over the 6350 test due to the fact that 6300s A- have a lower TDP, which makes me think that a 6350 is simply a 6300 with a higher voltage tacked onto it with some better silicon and B- 6350s do not come in a black version which means that you might not have as much leeway in overclocking it.
Upgrade proof... no, not really. Bulldozer and piledriver at this moment (FX series AMD chips) are 3-4 years old at this point. They still stack up due to their large headroom to OC, which is honestly most of the reason I'm still running my chip currently. As AMD and Intel come out with new chips, they're going to require new chip sets. New chip sets means you're going to need a new MOBO with the correct matching set. As of right now, "upgrade proof" if you jump to a 6300, 6350 means that you have the options of: 8320 (which actually gets beaten by a 6350 in most cases), 8350, 8370. You need a different motherboard for the 9000 series FX chips due to their ridiculous TDP. Which is most of the reason why I recommended grabbing a new Mobo and OCing rather than spending money on a new CPU right now that might be (even) old(er) news within 9 months.

Ideally... Yes, but at that point you might as well get a new system. If AMD Zen is what it's promising to be (Hyperthreaded cores, 12 cores, 14NM architecture) it is most likely going to outdo any FX processor out there. I will be incredibly sad if it does not. A good OCing motherboard will not be too much of a pocket digger.
This: http://www.newegg.com/Product/Product.aspx?Item=N82E16813131874
is the newer version of the board that I currently have installed in my machine, and OCing quite handily on. By way of Mobos, that is mid line for expense.
If your mobo is crashing as hard as you say it is, it will not be a bad investment to grab a new one and manually upgrade your system through BIOS in OCing your CPU/GPU, and in maybe a year or so look into a new one. Cause at this moment, your machine is probably 2-3 years old. Mine is 3 and yours has similar components in it. If your machine is on its last motherboard legs, 9 months is going to kill it. And at that point, it might kill other components in your system, so it'll be a better idea for you to fix the problem now instead of trying to wait it out and possibly killing more of your machine.
Another thought I had: what OS are you running, and how long have you been running it on? /where is your system installed?

If it were me, I wouldn't skimp on a case. Don't go crazy and get a Corsair Obsidian D900 (uuuuuuuuhhhh I need a towel), but don't leave yourself a $30-50 budget for it either. Lower budget means most likely plastic components, less air flow and design, less ability for cable management in the rig, etc.
Those temps shouldn't do anything to your machine honestly. I just ran Prime95 to test my machine at 4.2 for temps/long term stability and I got up to 65 degrees at one point in the night and nothing happened.
For your RAM, is it compatible with the MB/CPU?

With a 4790k... I mean, what you WANT is a 980 TI but I think that's most of your budget just dumped to your GPU. A 970 would be a good mid-high tier card to start with. In 2 years or so the price will drop and you can buy another, SLI them together.
$500 JUST FOR psu, case, mb, and hard disk space? Or does that include the i7 and GTX?

http://pcpartpicker.com/p/2QqCsY
With a 970 you hit your $600 limit before you get to your case or your psu :/