Don't change your mobo rather buy a decent core 2 quad processor. This way you will have enough for your kick ass gpu. You need a good CPU to get a good gpu otherwise the CPU will bottleneck your gpu.
Get a HD 7950 or a HD 7870 to play games at max settings.
P.S. AMD has already announced the HD 8000 series so if you can wait a couple of months for the cards to become a bit cheap.