I've been experimenting with an X2 myself.
It's wonderful in AoC @ 1920x with full shadows, bloom, full quality ground radius, the rest set to high and 12xCFAA|16xAF. I haven't noticed any horrid micro stutter and my min frames are more than double over my overclocked GTX 260.
, I have yet to regret the purchase.
My GTX 260 did fine in the above title and certain scenarios dropped it down to 18FPS with 4xAA active @ 1920x. That annoyed me to no end and made the game sluggish in said scenarios.
One of the best price vs performance options going @ 1920x with AA is HD 4850 Crossfire for about 300usd. On a similar note, I feel that res and up with AA is best for the X2.
DX 9 Warhead results are below for the X2 and others from Hardware Canucks-