Finally rep enough people to give you another +1 for winning that PSP/PS3 screen awhile back.
Looks like my case is finally shipped, though tracking isn't updated yet, so I don't know when it will arrive. However, I am assuming this Thursday. Also bought some AS Ceramique for my chipsets and 8800GTs.
I really do not know if the ceramique will help you at all. There is already a silver thermal compound applied to my 9600 GSO, so most likely your 8800s.
Worth a try I guess. If it doesn't help, you can always use shin etsu. It is the best for GPUs. Or AS5 since you have it.
I do have AS5, but AS5 is conductive, so I would have to be really careful with it if I used it. I was reading online, and they said AS5 and Ceramique is only about 1c-2c difference.
People told me to use MX-2, but that seems a bit much.