The difference between x8/x8 and x16/x16 is small.
The difference between x8/x8 and x16/x16 is negligible outside of benchmarks and some scientific computing apps that need to do massive amounts of communication between two cards or the card and the CPU.
The expansion slot area is identical to that of all the other Z77A series motherboards, consisting of two PCI-Express 3.0 x16 (x8/x8 when both are populated), one PCI-Express 2.0 x16 (electrical x4), and four PCI-Express 2.0 x1.
i Plan on using:
3570K - With Fan
7850 - Possible cf in the future
Antec HCG 620WM - Although im considering the http://www.newegg.com/Product/Product.aspx?Item=N82E168... for the extra W
Corsair Vengeance 2x4gb
In my Antec P182 Case. Also i don't know if there is a difference between how many fans you can connect, but i currently got 3 and space for one more.