i5 or i7

help me, i'm going to buy one or the other soon!!!

i5 for you unless your running multi GPU set up. i7 1366 is more futureproof, but seems overkill for your needs. i7 750 and a good mobo + ram and your good to go

I will be running sli!

I'd still go with LGA1156, you'll lose 5% from the 8x/8x bandwidth at most. I'd only go LGA1136 route if you go with 3 GPU's or more.

I find it helpful to look at it as 1156/P55 VS. 1366/x58, as opposed to i5 VS. i7. Although technically there is an i7 for 1156, the platforms themselves are not identical.
You can build a rig on either platform, which will be very good for gaming. If you can afford x58, do it.
What games do you want to max out?

Well the thing is the i7 comes in two flavors the socket 1156 or the socket 1366.
the socket 1366 uses the more expensive tri channel DDR3 RAM, socket 1156 uses dual channel. But both still have 4 cores and 8 threads. The i5 only has 4 cores and 4 threads
But it comes down to one thing, What is your budget?
Low budget? i5,
Mid to high budget either of the i7's

i5 unless you're going to be doing lots of 3d/video editing