i think
m5a99x evo r2.0 is based on AMD 990X chipset but m5a99fx pro r2.0 -on AMD 990FX chipset .The main difference is better support of SLI and Crossfire . The first both cards will run at x8 but on the second (pro) at x16 . But there would be no noticable difference . So go for evo.