None, as long as you do not XFire...
But the RD580 chipset compliments the X1900's, plus allow for XFire option later, if you choose...
Asus's A8R-MVP is the best one so far, imo...
But to be replaced with the A8R32-MVP next month, same chipset and ULi southbridge, but instead of 2x8x PCIe slots, you have 2x16x, and you get dual gigabit lans instead of one...
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