First of all let me tell you what rig ive got:

AMD Phenom II X6 1090T @ 3.9ghz
4GB RAM
Sapphire Radeon 5870 1GB

If I run the game on all 'Very High' I get 60 fps 99% of the time, resulting in a VERY smooth running game. However if I enable Tesselation (which involves changing two options in adv. graphics settings to Ultra) my frames drop to 30/40 fps.

Is this normal for a 5870 1GB? I dont see the point in having a dx11 card that cant handle dx11 features.