Yup, the 9800GT
is exactly the same
as the 8800GT (well, some
of the newer ones have a smaller 55nm chip, performance it 100% the same though).
If you upgraded from an 8800 GTS 512, 8800 GTX or 8800 Ultra, your performance is now lower.
If you upgraded from an 8800 GTS 320/640 your performance is just a tad higher.