
Yes 8500LE is def the card you should go for and 128MB if you can get it, the only advantage of going Rad9000PRO is that it can be used fanless (although Rad9000 is more common) and hence will run very quietly. From slowest to fastest the Radeons break down like this:
Rad7500 = GF2GTS/TI perf and like them is DX7
Rad9000 = Rad7500 but with DX8 and slightly enhanced DVD/MPEG playback, image quality and standardised dual display
Rad9000PRO = Same as the Rad9000 but a good 20% faster
Rad8500LE = Much like the Rad9000PRO but is 15% faster, again DVD playback and image quality are slightly weaker but still VERY good
Rad8500 = Same as Rad8500LE but 10% faster

Clock speeds will vary by manu and oem/retail but only usually by about 10% tops, also non-Rad9000 cards may not have dual RAMDACs needed if dual display is important to you. So anyway on to GeForce:
GF2TI = Rad7500 (ie DX7) but with much poorer DVD playback, image quality, dual display and TVout.
GF4MX = Enhanced GF2 so still DX7 but now faster and with enhanced DVD playback, image quality, dual display and TVout, MX440 is a good deal faster than GF2TI.
GF3 = In 3D perf very comparable to Rad8500 cards (hence also DX8) so a good deal faster than Rad9000 series, GF3 are let down by image quality, dual display and TVout although they are generally improved over GF2 they do vary by manu.
GF4TI = Enhanced GF3 (so DX8) and are faster with much imporved image quality, dual display, TVout and a great ability to get the most from the top CPUs. Other than the odd turkey, manu makes VERY little diff.

Comparing Radeons to GF we see the Radeons have significantly better DVD playback and TVout, and for the GF2/3 cards much better image quality too.

So all in all, Rad8500LE-128MB will definitely perf better while the Rad9000PRO should run a bit cooler and quieter (esp if found fanless), if you'll be running a 750mhz CPU for a good while yet there will be very little perf diff between these cards. I'd dismiss the GF2/3 straight away, the GF4MX are inferior to the Rad9000 series and the GF4TI are overkill. Rad8500LE-128MB or Rad9000PRO in either 64MB or 128MB form are by far the clearest choices IMHO.