The motherboard I will buy will only support x8 x8 crossfire, I want to know what loose of performance I get. And I se that the GPU are far apart, will I be able to connect both cards?

Mobo: http://www.newegg.ca/Product/Product.aspx?Item=N82E16813131402

GPU: http://www.newegg.ca/Product/Product.aspx?Item=N82E16814102864

wtf didnt we already tell you this O_O
5770S WONT LOSE ANY PERFORMANCE
0
NADA
FUCKEN ZERO
wp

Yep it'll be fine.

Just a heads-up: If you buy that mobo and you care about the internal looks of your PC (ex. if you're getting a see-through side-pannel), the theme of the motherboard is a blue (some parts a sanded chrome finish kind-of look). So if you are choosing some sort of LED look, blue might be the way to lean.

Anyways... speaking about practicality... x8/x8 will be entirely fine. Completely.

If you're operating at 1680x1050 or lower, you should only need one 5770 though. I'd suggest you go with dual 5770's only if you are operating at a higher resolution, or want to future-proof yourself. If it is future-proofing you want, you may want to hold on to a single 5770 and considering upgrading to an entirely different card with that $170-ish saved in a year or so down the line.