Prices are not going to drop on the 11th. I can't tell you what is going to be released on the 11th, but if you want to head on over to TheInq.net, they mention what will be unveiled at QuakeCon.
If your client wants a 7800GTX, just get it for him now. Prices are more than likely not moving until NVIDIA has some competition with ATI's next-gen cards, and those are going to be a while considering that CrossFire apparently won't even hit the market until September.