I would choose the 2550k, it doesn't have integrated graphics so you can achieve higher clock speeds. Plus, you get more transistors on the chip than the 2500k because of the lack of integrated graphics. I'm assuming you are upgrading your PSU and video card as well, if no video card than you should get the 2500k because of the integrated graphics processor. Although the IGP will not play SWTOR at max.
To summarize I suggest a new GPU, PSU, and a 2550k. (And MOBO if you don't already have one) I also would suggest the corsair H80 or H60 for you CPU cooling so you can have a more stable OC (liquid cooling does not have as much temperature fluctuation as aluminum heat-sinks.)
The 2550K is 100 MHz faster than the 2500K and has no IGPU so there are no native graphics. If you're a serious gamer the 2550K is a better gaming chip as you will be using a discrete GPU. But the difference is minimal.
just to clarify, the 2550K just has the graphics core disabled. it's physically still there. some believe this may provide higher clocks, i believe it's just a way to squeeze more money out of the consumer. unless you want the absolute maximum overclock, i suggest saving the $10 and putting towards an aftermarket cooler as bestlink101 suggested.
Ok so it still seems up in the air for now. So how about this, how much better would the i7-2600k, i7-2700k, or i7-3930k be when compared to the 2500k? And are the 6 cores worth having for the future when we start really using them? Should I forego them for a cheaper processor??
@Schube30 The information you are getting regarding the 2550K is assumptions and not accurate, the 2500K is a much even across the board overclocker, I actually know from my own experience, because I own both and have individually tested both.
I already had the 2500K and bought the 2550K to upgrade my wifes platform, but if the 2550K was a better overclocker I was going to keep it myself and give her the 2500K, the 2550K is a horrible overclocker very tempermental, so my wife gets the 2550K as planned because I won't be overclocking her new build.
She is not getting my 2500K that bad boy is staying right where it is!
For overclocking purposes I 100% recommend the 2500K over the 2550K! Ryan
FWIW, using the 2500K with its HD3000 integrated graphics I played SWTOR on max settings (with shadows and AA turned off) on a 32" HDTV with a 768 resolution and it was smooth as butter. That said, I did overclock the CPU to 4.5 and the integrated graphics to 1450 before doing so.
If you're using a 1080 monitor, you'll probably be stuck on low or medium settings.
That being said, I got a MSI 560Ti and now I'm playing BF3 on max settings and I haven't logged on to play SWTOR since .