It's still better to go for a single card solution. Dual Card solutions are kind of like a hit and miss, but a better single card is guaranteed performance!
How about the 7950 [It's available for 220$ in US]
does this motherboard support 2 of them MSI Computer Corp. Motherboard North Bridge AMD 970 & South Bridge AMD SB950 Chipset ATX DDR3 800 AMD AM3+ Motherboards