to clarify you cant "use" hyperthreading, you just spawn more threads than the cpu has physical cores. Essentially what HT does is double the speed at which the cores can switch between threads (because at any given time even while idling you'll have 50+ threads running), the downside is that it always HAS TO switch which can cause performance loss if you have one very intensive thread that would move quicker if left alone by HT.
Modern pc games usually have 1 thread for sound, 1 for fetching, a bunch more for other random crap and a dynamic number of threads for rendering. Theoretically giving that dynamic number a high value would result in utilization of HT. Problem is though - the only time when you benefit from HT is when your cpu gets filled to the brim with heavy threads and gets bottlenecked by source material, since all the games threads have to be in sync and get the same face time but not all of them utilize the CPU to the max there will always be some slack in the delivery that negates HT benefits and instead you get the heavy threads harassed by HT for no reason.
That said 2500k will last you a long time for gaming. If you look at the specs game companies are producing stuff for - its rather depressing. Most commercially successful games on PC are console ports and will run easily on half a decade old hardware and the trend is on the rise. Of course you can wait half a year for ivy but i can guarantee you that there wont be any difference gaming on SB vs gaming on IB. Oh and as for 2600k - its a terrible waste of $100, you would get a much better bump in performance spending that 100 bucks on cooling or video card.
Edited by hazarada - 11/17/11 at 2:02am