The i7 960 is a quadcore with hyperthreading - meaning it can process eight logical threads simultaneously. This would help a lot if you're doing video editing (or with any heavily-threaded applications), but otherwise does nothing. The 900 series also uses triple-channel memory (for Socket 1366) so you have to buy three sticks of RAM to fully unleash its performance.
The i5 2500k and i7 2600k are both quadcore, but the i5 does not have hyperthreading. Again, this only makes a difference for heavily-threaded programs. If your computer is for gaming, you'll never notice a difference. Also, the ones ending in K can be overclocked very easily (since the multiplier is unlocked). The i5 2500k is only about $200-220 online, and the extra money you saved over buying an i7 960 can be used to get a faster graphics card and more RAM.
If you're balls-to-the-wall for more video editing performance, get the i7 2600k. Otherwise, stick to the i5 2500k.
I would mostly be using my computer for gaming, maybe some light video editing, and hosting servers for a game called "Minecraft." It's not a very graphic rich game so I guess i wouldn't need the hyperthreading?
3D Rendering, CS5, movie editing, huge spreadsheets or database number crunching, CAD are areas where the HT and triple channel memory benefit from the 1366 platform .... for gaming 1155 is the way to go.
Hmm you guys kind of completely skip over P67 vs X58. From what I've seen, P67 is good but you're still limited to 16 PCIe lane bandwidth, so for multi GPU configs you really should try finding a mobo with NF200 which doubles that bandwidth. I'm also not exactly sure how P67 enables SATA3(6gb/s) but on X58 it uses a couple of it's 32 available PCIe lanes.
Still, P67 and P68 are good enough usually. I'd actually like to see a good mobo breakdown of the differences.