Ok, well I believe a stock geforce 3 runs at 200 mhz core, 230 mhz memory.
From what I can find, xgpu runs at 233mhz core(I thought it was 200, I know it got a downgrading from the original rating), with 200 mhz ddr memory.
I believe geforce 4 speeds are something like 300mhz core, and 300 mhz ram.
Geforce 3 TI 500 runs at 240 mhz core, and 250 mhz memory.
Geforce 3 TI 200 ruuns at 175 mhz core, 200 mhz memory.
So the xgpu has higher fillrate and other features over the geforce 3, but lower memory bandwidth, made even lower since it has to share bandwidth with everything else. I guess you could say the xgpu has a good performance advantage over a geforce 3(but it's not the huge difference people make it out to be, it still isn't geforce 3 ti 500 level), but if it's bandwidth limited, it probably wouldn't be faster than a ti 200.(guess it wouldn't be bandwidth limited unless it does hdtv res or aa, and really not likely to reach bandwidth limit if it goes heavy on pixel shaders).
I don't personally, I would choose a geforce 3 in the xbox over the xgpu if it meant having halo with ut2003 like graphics at 60 fps over halo graphics.(assuming the pentium 3 would be fast enough to get it up to 60 fps)
I'm still just a little peeved that from day one since I had my ti 200, I found out it wouldn't be able to actually use any of those fancy pixel shader effects it had and maintain 30 fps.(well, it sort of did, I put it in a second computer and it runs halo at a pretty much solid 30 fps at 640x480, but looks horrible compared to my radeon 9700 pro at 640x480)