Socket 1366 mobos are a bit more expensive.
If you want something more future-proof, get a socket 1366 mobo with sataIII and USB3.0 (there aren't many out there, I think Gigabyte is just about the only one that makes one like that right now... maybe Asus too, haven't looked recently), and an I7-920.
If you want something cheaper that you can replace sometime in the future, get a socket 1156 mobo and a I5-750.
Realistically, especially at higher resolutions (1680x1050 and higher), you will see negligible to no improvement between the I5-750 and I7-920 and I7-965.
However, you will see more of a difference (especially in minimum framerates) between an I5-750, and say... Q6600 or E6600 or Phenoms. It's somewhat situational, but it is there.
Most of the time, the video card is the limiting factor. Sometimes, it's not.
P.S. Oh, by the way no matter what processor you get (i5, i7, whatever), definitely overclock it to 3.6ghz at least. It would be a shame not to. You should be able to do 3.6 just fine even with the stock cooler...