I've just received my visiontek geforce4 ti4600 today upgrading from a geforce3 ti200.
I can't say there is any difference in IQ between the 4600 and the ti200 at least to my eyes.
They both have the same IQ even with AF and AA.
Of course the 4600 is soooooo much faster. Everything runs so smooth.
I've seen the Radeon 8500 in action and I gotta say I like the geforce 3/4 IQ better specially with AF.
Anyway I think you will be satisfied with either the radeon8500 or the geforce4 ti4200, both cards perform well and have great image quality.
Sometimes I hate being right everytime.