I just ran across something that could be just a total coincidence but I tried it three different times and I got the same result.
I have a 5970 installed in my machine and because I can't stand leaving things well enough alone, I had done a very minor overclock from the stock 725/1000 to 750/1050-yeah I know, not much! While I was piddling around resetting all the graphics goodies, I realized that since I installed the 5970 I had NEVER o'clocked the secondary GPU--only the primary GPU.
I matched them both at 750/1050 and cranked up ROF. I noticed a verrry slight, almost stutter when I looked around my aircraft so I tried something to see if it would be more noticable. I shot down a plane and went to its external view after it crashed and was burning and I had noticable stutters when I panned around the burning aircraft. I left the primary GPU at its slightly overclocked settiing and set the secondary GPU back to the factory clockspeeds and repeated the test-----smooth as glass!
I'm sure it's just a coincidence and probably total cr@p but I did it THREE times both ways and it repeated itself EVERY time. I can't begin to imagine what could cause this other than some kind of timing issue between the two GPUs. Go figure...

At first I thought it was the new drivers because I've had smooth gameplay for a long time. After setting things back to the previous overclocking settings, it's all good again!
