I think the 9700P may still be the better buy, but it's a much closer race now. A 9700P is basically a 9800 with very slightly faster memory. So you can check out recent benchmarks of the 5900 and 9800 to compare the two. Firingsquad has a lot of those. Digit-Life, Hardware.fr, and NordicHardware should also have 9800 vs. 5900 benchmarks.
I'd choose the 9700P for its better AA quality and DX9 performance, but it's a close call, and one you'd do well to research. (You can start with Anandtech's own high-end shoot-out to check if one architecture is noticably better at a game you're interested in--in some games, currently one card may be faster or less troublesome than another.)