Since the graphics subsystem of amiga os is not fully unified (we have different, unrelated systems for 2D and 3D), I'm not really that surprised that things like this are possible.
The only 2D aspect I can think of that would affect 3D games would be blitting speed (for windowed displays) and screenbuffer switch times (for fullscreen displays).I very much doubt that there would be any significant difference between the two cards for these jobs. Blitting and framebuffer switching tend to be more than fast enough on any half decent graphics card ;-)
