I have both a retail Radeon 8500 128MB @ 312/301 and a Geforce4 Ti4200 128MB @300/540. Catalyst 2.5 vs Detonator 41.xx. If I turn down the quality settings on both, the Radeon gets 160fps and the GF4 gets 210fps in Unreal Tournament at 1600 x 1200 x 32 bit. Turn on the anisotropic and put all the sliders to quality and what not, the Radeon runs 110fps and the Geforce4 drops down to 100fps! It's a close call, but generally the 3D image quality is slightly superior on the Radeon, while 2D text is definately better. I prefer the Radeon hands down, though until now I had a slight preference for Geforce.
Another thing is the 128MB issue, it really isn't needed now and I think buying it for future proofing is silly. By the time there are enough games out there that really need that much video memory, the current crop of video card will be obsolete anyway. I only picked up both of these 128MB cards because I bought them refurbished at newegg for $99 (Radeon 8500) and $117 (Geforce4 ti4200.) For someone with an adventureous spirit I would suggest finding a Radeon 8500 LE 64MB for dirt cheap, under $70. Just make sure the RAM is rated at 3.6ns or better. Go here
voltage mod and learn how to replace two resistors on the card. Just make sure that you 8500 LE follows the reference board, I would get a built by ATI to make sure. Flash the bios to revision to 1009, in my testing it allowed me to overclock my memory (Infineon 3.6ns) to 315(630MHz) when it was hitting 299 before. This bios also allowed me to get the retail 8500 128MB to run 315 also, but the card was only recognized as a 64MB so I flashed back to version 7006. Now for $70 my son is fragging bots at the same fps as me whether or not I am using the retail 8500 128MB or the Geforce4 Ti4200, absolutely amazing. Unlike most of us (including me) he doesn't need bragging rights for a nice piece of hardware, just results and this cheapo solution delivers! I'm gonna mod two more, upgrading my wife and daugher from their Radeon 9000's.