I tried anisotropic filtering in opengl on my ti4200 but had difficulty telling the difference in wolfenstein and quake. there was a noticeable improvement in medal of honor but it was a bit slow. the reasons why I got the gf4 over the 8500 is because the antialiasing is a lot faster, the drivers are better and it overclocks pretty well. Its a good bit cheaper in the UK too.
I had both a gf2 gts and radeon 1 at one point and found that the gf2 had terrible 2d quality in both desktop and dvd quality in comparison to the radeon. The gf2 was faster but this margin reduced with newer drivers. the xfx ti 4200 has easily as good 2d image quality as the original radeon
I would say get a ti 4200 because the image quality improvement/speed tradeoff by quincunx antialiasing outweighs other benefits that the 8500 might have in anisotropic filtering.
Athlon XP 2800+
1 gb DDR sdram
ATI Radeon 9700
120gb IBM HD
Audigy 2 OEM