Re: AMD Phenom x6?
AMD's research indicated that games that don't use all the cores in a multicore processor will still benefit from having 3 cores active. They then overclock those 3 cores to a predetermined clock speed, usually within the specified thermal envelope for that processor (the TDP) to achieve a performance improvement.
Depending on what you have now, and the games you play, the 6 core Phenom II is either a great idea, or a waste of cash. Unless you play multithreaded games all the time, it's better to stick with a really fast dual or even a quad core.
I play a lot of games - WoW, Supreme Commander Forged Alliance, L4D, L4D2, Eve Online, Far Cry 2, Call of Duty 4, etc and I have yet to make my Phenom II 940 (a quad core) beg for mercy. I even do heavy video work with Adobe Premiere. You'll get more performance in games with a good solid processor, enough RAM and a high end video card. If you do a comparison between the Intel CPUs, even the might 980x, you'll find that with the same video card, at the higher resolutions, the performance is identical to some of the slower Intel and AMD CPUs (depending on game tech of course) but for the most part, that's how to value your system upgrade goals.