rockycrrab :
Thanks for the reply!
The reason why I didn't go with the 2500K is because I don't need to overclock. Even though I do play games, the most taxing game I have is Battlefield: Bad Company 2, which could run maxed out on a 5770 and there would be no need for a CPU overclock. Therefore, I settled on the i7, since the extra threads will be useful in the future when programs utilize more threads. I don't think overclocking it to 4GHz will make any difference for me for my uses. A 6950 would be overkill since I play games mainly on my wii/xbox with family. Also, I don't upgrade often (my current computer is still a Pentium 4 Northwood!), so being a bit "future-proof" will help.
Your right, I should go with a micro ATX board if the need arises. I just thought that the extra slots might be useful in the future, but currently I have no plans for it.
I think I will go with the Z68 since the prices are pretty similar
Hyperthreading makes use of unused parts of the main core to dispatch a second task. The hyperthread task does not have the full compute power of the main task. It is, perhaps, the equivalent of 1/4 of a full core.
These hyperthread tasks only come into play when there are more than 4 threads(on a i7 cpu) available to be dispatched. If your app can consistently dispatch 8 or more threads, then you have the equivalent of a 5 core cpu running at the stock multiplier. 3.4 in the case of the 2600.
If, on the other hand, you have a 2500K with a mild oc to 4.0, you will have approximately the same compute power.
90% of 2500K chips will oc to 4.0 or better. 50% might reach 4.5.
If you still really think that multiple threads will be useful to you, consider spending an added $25 or so for the 2600K to preserve the OC option.
Some arguments for the 2500K:
The 2500K will be $100 cheaper than a 2600 to start with, and better since you do not now need to OC.
The 2500K will do better @4.0 when there are 4 threads or less to be dispatched.
By the time future apps that you use are capable of using many threads, your "future proof" 2600 may well be obsolete.