Yeah, the next gen cards from ATI aren't going to be anything to shout about due to them being around the performance of the already released 7800GTX. If you want to wait for the best next gen card, wait for either the nVidia G70 Ultra, or the G72. Unfortunately, they are due for release sometime late next year.
So my advice would be to either go with the 6800 GT, or if you want to stick with a graphics card for quite a while, get the 7800GTX. Depends how much you are willing to spend!