The G4 cube was AGP right? I can't attest to the AGP version of the 6200, BUT I have done the reflash of a 6200 PCI for my B&W upgd G4 450 machine.. It's got the 66 mhz pci slot for video and it works great! OSX 10.4.9 gives you OpenGL on that card, and I've taken that machine to 10.4.11 with core image support and open gl. The 6200 is a nice fast board for the now older mac and yes as stated above, they are getting very cheap to obtain.

Anyone have any clue on OS 9 video drivers for the 6200? I get 256 colors in multiresolution and that's all under 9 but full usage under OSX.

Good luck!