
Depends what you mean by 3D modelling. Anyway the cards break down like this:
3D perf:
GF2 - Getting on now and not worth it considering the cards you can get for $10-30 more. GF2TI is a good 50%+ faster than GF2MX.
GF4MX - Enhanced GF2 cards. GF4MX420 is a fair bit faster than GF2MX, GF4MX440 is faster than GF2TI and GF4MX460 is faster again.
GF3 - Bring much better perf, AA, AF and DX8 hw over the GF2 and GF4MX cards. TI200 is a fair bit slower than TI500 but can o/c to VERY near TI500 speeds.
GF4TI - Enhanced GF3 (so DX8 hw) with much better perf and really take advanatge of the faster CPUs. TI4200 is faster than GF3TI500, TI4400 is a good 10% faster than 4200 and 4600 is 10% faster again.
Rad7500 - Near enough GF2TI level perf and much like it is not DX8. Like all Radeons actual speeds can vary (10%ish) by manu and also oem/bulk vs retail.
Rad9000 - GF4MX440 perf but has DX8 hw. Rad9000PRO is faster giving GF3TI200 stock perf but lacking the AA.
Rad8500 - Near enough GF3TI500 level perf again only lacking in the AA dept. Rad8500LE is about 10% slower than the Rad8500.
Rad9700 - By far the fastest and most capable card out there and the first to offer DX9 hw. Usgae of DX9 is likely to be at least a year away but in terms of sheer 3D perf, AA and AF there is no card which comes close.
Other abilities:
GF2 - Nothing to note. Very poor image quality (IQ), poor TVout and no dual display.
GF4MX - Hugely improved IQ, better TVout/VIVO, dual display and hw DVD playback.
GF3 - Slightly better IQ, esp with some manus. Like the GF2 poor TVout and no dual display.
GF4TI - Great IQ, like GF4MX improved TVout/VIVO, dual display but no hw DVD playback.
Rad7500 - Like all of these Radeons, great IQ, great TVout, hw DVD playback and dual display is very common but some manus ommit it.
Rad9000 - Same as 7500 but slightly better IQ than the 8500 and less variance with manu. All should have dual display. Also improves DVD (and some MPEG?) playback.
Rad8500 - Same as the 7500 but with enhanced IQ.
Rad9700 - Once again same as 9000 but even better IQ and improved DVD/MPEG playback.
Tweaking by o/c'ing:
GF2, GF4MX, GF3TI500, Rad8500, Rad900PRO, GF4TI4400 and GF4TI4600 are all likely to gain no more than 10%.
GF3TI200, GF4TI4200, Rad9000 and Rad8500LE all gain a good 15%+ from o/c'ing.

This was meant to help and make things clearer when I started, now I've finished maybe it doesn't. HTH though!