I am quite sure that 2x 9800GTX2's is still a normal SLI since they are technically each only 1 board still.
In some situations only. Alot of the time the 4870X2 will beat the 3 280GT's... Keep in mind that the only difference is that 3 280GT's have more RAM, yet the 2 4870X2's have faster RAM with more shaders.





