In synthetic benchmarks a 9800 Pro tests about the same. In actual 3D games,
it's typically 10-15% better at most. It doesn't really leap ahead at higher
resolutions either. An X1600 Pro is a 128bit card, 500Mhz core with pretty
slow 395Mhz(790) DDR2. The 9800 Pro is a 380Mhz core with 340Mhz DDR2 (680).
The 256bit memory interface is a big deal. It's why the 9800 Pro keeps up.
They're both DX9 cards. Not really a worthwhile upgrade. An X1950Pro or
7800GS AGP is a dramatic jump. An X1600 Pro and 9800XT (within 5% of a 9800
Pro) are compared below, along with quite a few others.
http://www.hardwaresecrets.com/article/337/3