hello , i got low fps when i use crossfire and to my surprise with just one graphic card i got very good fps (all games are running better with 1 graphic card). I asked a lot of people and they told me that is possibile to one card is running on pci x8 and the other one is running on pci x16 and i should change both to x16 from bios. The problem is im really nab in bios and i have no ideea how to change this.
I have x2 amd radeon hd 7770
Motherboard : ASUS : F1A75-V EVO
Your cards should be in the white and the blue slot, not in the black one. Concerning the bios settings, consult the mobo manual. It has all the details. You can not set both slots to x16, because it supports only x8 with two cards, but that doesn't matter.