I ran a small test on the Semper Fi or Die mission for my pc. The level after the entire southern area of Manhattan (I think) gets flooded and there is water everywhere. I use an intel i7 core 870 clocked at stock speed and an amd radeon 6970HD 2GB graphics card all set at stock speeds and in this area up until the first wave of aliens drop in I was averaging 30 to 50 fps without looking into the sky.
What are you guys getting on this level? I'm keen to know!