I cant help with your mobo, but if it can run them, i would choose an ati card.
I wouldnt choose the 5k series now. Even tho the 5870 is still a buttkicker card, the 6870 can do 85-90% of its performance, eats less energy, plus cheaper than the old monster.
The 6950 is also a good choice, i heard with its duel bios, it can be turned into a 6970. Pretty much better cards than the geforce 570 series, not to talk about they are cheaper.