Choosing a CPU / Motherboard to add to an older system

I am looking at spending roughly $400-$500 on a CPU / Motherboard combo. I will be adding to a system I build 6 years ago. Keeping the Antec 900 tower, three hard drives that are all pretty average, have 4 1 GB sticks of PC 800 Ram, fans, disc drives and a Radeon 5670 graphics card that I added a year or two ago.

I would like to find a combo that will last a while and like the possibility to upgrade later either to a better motherboard or a better CPU. In essence, I don't mind having either the MB or the CPU be higher end than the other. I am currently running a core 2 duo (I think it's a 6420). I had a crappy MSI board that it came with that I ended up replacing three years ago because it died. Also replaced my GTX8800 when it died (with the Radeon). I really only play World of Warcraft when it comes to gaming. I hate getting low FPS during raids or when I'm running other applications in the back ground. I really notice a performance drop in raids, when I run medium video settings and or running stuff in background while I'm playing on lower settings. I will be using a samsung 24" monitor that is native resolution at 1920 x 1620. It's refresh rate is 60. I will also be occasionally converting video - from my old Hi-8 camera tapes (and other formats) to DVD. Currently this takes forever with the Core 2. If I get a blue ray burner, I may want to put downloaded movies or other stuff on blue ray. Other than that, my kids surf the web, watch streaming video etc.

I was thinking of going with either the 4770k or 3770k Intel processor. Have no clue on the MB. However, i was reading a recent Tom's article about the Sandy Bridge E. It intrigued me because the author mentioned that it's design would affect performance on World Of Warcraft. I thought that may be a better way to go because I could get the low end 4820k or 3820k and a decent board for similar investment as the 4770k and 3770k. From what I've seen, looks like the older 4770k and 3770k are faster...is this true? I don' t really understand why the newer processors would be slower because the specs seem similar... I don't really understand the importance of the different types of cache, memory lanes all that stuff...

Please note - I don't intend on running more than one monitor, or more than one graphics card. It's possible that would change and it would be nice to have options but I will never have more than 2 graphics cards or more than 2 monitors.... that just seems extreme to me. I'd probably just go one big screen and 2 cards if I had to. I don't know what the cut off is when I'd need a 2nd card to accomodate a larger screen.

I will be using windows 7 pro and keep all the other stuff I have. I'm open to getting new memory if people think it's going to make a difference - for example in loading web pages, game loading etc...Also, I'd consider a solid state drive if it's not too expensive. I'm thinking I could just load the OS and games on that drive and keep the videos / music / photos on the others. I feel that the graphics card is sufficient for my needs at this time, so i'm planning to spend everything on the MB/ CPU and possibly memory and or a SSD. But priority on the drive is pretty low at this point.

Also, I don't see myself as being a person that will over clock so that feature may be fun, but also may never be utilized.

Basically, I want to get something that will last a few years like this current system did and not suck. Something that will be pretty fast doing what I want to do and allow me to play my addictive game with all the settings up hi and not bog down. Who knows, my kids may find a game or two they like, but for now they are on XBOX I'm on PC.

So, help me select a CPU -- prefer intel (no offense to AMD users). From what I"ve seen Intel will not get as hot, use less power and be faster ( I don't mind spending an extra few bucks for these features). I don't know if it's better that the CPU is higher quality than the MB or vice versa. Like I said, if there's a combo deal for example that the CPU is really nice and I'm getting an entry level MB that's ok. Ideal situation is I spend $400. But, I have the money for more and would step up if I think I'm getting a good deal and or better performance / lasting power. I thought about a refurbed CPU from Tiger direct, but honestly I would like to be able to walk in to a store (such as Fry's) and walk out same day with my toys in hand and go put them together.

Thanks for the replies! I was considering LGA 2011 and the Sandy Bridge E or Ivy Bridge E CPU options, just because I thought it'd be nice to at least get on the newer platform. Toms had an article describing the Sandy Bridge E that was related to World of Warcaft I thought I'd get a somewhat entry level i7 of one of those two. I also looked at the 4770k because it had good reviews. I want to be able to do video conversions .... not sure if hyperthread is important for this.

I didn't realize i'd have to get RAM, thanks for informing me. There is a Fry's very close to me, but I've never shopped at Micro Center. I think there's one of those close by as well so i'll check it out.

If I understand correctly, i7 4820 is the newer, Ivy bridge E and i7 3820 is the Sandy Bridge E... i7 4770 is the Haswell.... if choosing between these three which one would be best? It seems to me they are roughly all the same cost - at least for the CPU.

I guess the real question is... will this new architecture / memory lanes etc. really matter if I'm only going to run one graphics card? If i'm running WOW and other applications in the background does that make a difference?

Fry's has a sale on a 4770k with an MSI z87 G45 board. It's 449 after rebate. No need to post online offers, I'm either going to Fry's or Micro Center. http://www.frys.com/product/7872659?site=sa:adpages%20page1_FRI%20date:100413

Thanks again!