The GX2 with hacked very high in DX9 gets about 50fps @ 1680 when OC'd. Game play is a little less than that. Runs 30-45 fps at the beginning and 20-30 in the ice and on the ship. Too low for me.
I run it at all medium except for shaders, textures, water and sound which are high. It stays above 45 fps most of the time avg around 60. If you want to run very high under DX10 you will definitely need SLI/CF GTX260/4870 or above for it to be playable at all.