That's a socket 1156, which means that you can put a Core i7 in there, but only Nehalem and not Westmere or beyond. Going with 1366 allows you to upgrade to Westmere or beyond (6 or more core) in the future, should you desire. 1366 will also require 6 or 12G of memory, since it's triple channel. You can't have 8.

That said, I went with an 1156 Core i7 and 8G of RAM. I don't expect to update the chip in this board -- I'll get a new board if I want a Westmere. The i7 is just a bit slower than that i5, but it has twice the cache at 8M. That will more than make up for the slower clock speed for typical application performance.