I often get very good fps, the first 10 minutes, like 130-140 in cockpit, 150-170fps outside views, then suddenly it drops to 50-60 fps, flying over big towns goes pretty bad somethimes though, but it's just weird I get insane fps at the start. Not using any profile I'm aware off.
i7 860@3.93Ghz, 2x 5870, 8 gig memory.