I upgraded my Dual 500 MHz G4 (AGP 2x) from the Apple OEM Rage Pro to the OEM Radeon 32 MB DDR and it made a world of difference in OS X, but seemed to make less difference in OS 9. I suspect that this is due to the apparently negligible support for the Rage Pro in OS X that some people have stated. I don't know, I haven't seen the precise issues they claim. My ATi Rage Pro PCI runs my 2nd monitor with ease and has not had any problems thus far.
The other reason I would venture to guess is that OS 9 rarely took advantage of my 2nd processor, so perhaps the CPU was the bottleneck, not the graphics card. In OS X, most everything uses the 2nd CPU, so now the card is the bottleneck, not the CPU.
All I know is that in Giants (OS X 10.1.1, of course) my Radeon gets me 15-25 fps at 1280 x 1024 and my Rage Pro gets me 2-5 fps at 800 x 600. Both of these are the AGP cards (I never tested my PCI Rage Pro, just the AGP one), and except for the resolution, all settings were the same.
In the Return to Castle Wolfenstein test (both the 1st and the 2nd), I get from 40 to 80 fps at 1280 x 1024 with mostly maxed settings on the Radeon. Keep in mind that the tests do not support multiple processors, I have to manually turn it off. I expect this game to absolutely cruise when it hits the shelves.
All in all, I'm very happy with the Radeon. It also beats out the GF2 in most tasks. Check <a href="http://www.innermac.com
</a> for a very thorough review of the two cards. Don't believe that crap at CNET either... their review of the two cards was mostly bull.
Sidenote: I sure wish innermac (intentionally spelled all lower-case) would update their site with new content. They really do a good job on the stuff that they have done so far. Very objective and quantitative analysis of the subject matter.