I'm looking at the same issue myself. The 7900GTO seems like the sleeper card out there and is already pretty cheap. Retail prices probably won't come down too much. I know it took almost a year for the 6800GT prices to decrease enough that it was relevant.
So, if you want a 7900GTO then I don't think you'll be kicking yourself in the ass two months from now because the price dropped $100, it will probably drop just a small amount.
What I'm hoping is that when a bunch of folks jump on the 8800's there will be a glut of great, used, high end 7900 series on the market and the prices will be fire sale cheap.