I have a GA-970A-DS3 motherboard with a HD 7770 running as a single GPU. I've just upgraded to a high resolution monitor (1920x1080), and I'm thinking of dropping in another 7770 for the extra performance in a couple of weeks.
I think with the PCI-E lanes available, this motherboard should support CrossFire. However, I'll have to go with a x16 x4 pairing. Will this effect performance significantly?
Well you're always welcome to try it, but here's my thought:
You will lose at least 10% on average over the best case:
That puts you down below 7850 performance territory (which is about the 6970 on that graph). Combined with the issues attendant to a crossfire setup (driver headaches, microstutter, etc), I think you would be better off selling your 7770 and picking up a 7850: The resultant cost shouldn't be much more than the cost of adding a second 7770 and the resulting experience will be much better for you.