No games take advantage of 6 cores. I would save some money and drop down to and AMD Phenom™ II X4 or better yet, use that extra money for an i5 2500k and appropriate motherboard. Most games don't even use 4 cores either.
I would only go with a 6 core CPU if you use programs that you know will use them all like a video encoding program.
If you already bought your computer, then nevermind.
The difference between the AMD Phenom II X6 and the AMD Phenom II X4 is only $40...I don't see why I shouldnt just go for the 6 core.
jaguarskx has already told you. No games out there in the market for now, take advantage of 6 cores. This is the beginning of the 4 core generation.
Phenom X 6 can be handy, only if there are apps or games, that make use of 6 cores. But currently there aren't any.
I understand the reason, but it's only $40. That's nothing. It would just make more sense to pay an extra $40 for the six core even if i dont end up using it until later. I mean, $40 is like 1/6 of my weekly paycheck.
For and extra $80 - $100, the i7 2600k will give you an extra 100MHz and Hyper Threading technology. The extra 100MHz can come in handy in games, but not Hyper Threading. Games do not take advantage of HT, just like they will not make use of all 6 cores in the AMD Phenom II X6.
Overall for games, the i7 2600k is faster than the i5 2500k at stock speed by 0.1GHz, but that is not worth the premium you're gonna pay since the i5 2500k is easily overclocked.