I got firstname.lastname@example.orgGHz , win7 x64, 4gb, 750w psu and 4870x2 with 10.6 drivers. When i run all on high i noticed when tank grande or luncher explodes near me and player should get the deff effect FPS drops from like 45 down to 28-30. With HIGH and MEDIUM graphic i get the "lagg" effect all the time, i got 30-40fps but it feels like playing slideshow all the time. I turned on loging of GPU utialization and noticed again strange thing, sometimes happens that GPU1 utilialization jumps to 97-96% , GPU2 30-40% BUT CPU utilialization drops from usually 85% down to 60%. Then i usually get framedrops. Usually both GPUs are working at same percentage till 50% utilialization, but then 50% is passed by GPU1 GPU2 doesn't follow with utilialization, it's left behind. I have game profiles installed. When i switch to LOW i get normal fluid gameplay.
I thought my CPU is problem but hey i don't have that BAD cpu and it's even clocked to 3.2GHz, but friend with Q9550 on stock and 5970 doesn't have these kind of problems on high.
This looks like driver issue to me, what do you think?