if the price is the same to you, then its pretty much your choice.
what would you prefer?
A. Get 2 8800GT and SLI them and outperform an 9800GTX?
B. Get 1 9800GTX and not have if perform as well, though it should still run most games on max settings, if not then at high settings, and when it starts to be slow to you, get another 9800GTX and SLI them.
Your choice.