The reason Bryce runs slowly on any particular computer (be it Windows PC or a Mac PC) is because it does all of its work (the rendering) in the CPU. It's all fractal math, so the better math (FPU) CPU you've got the faster Bryce renders. Fancy GFX hardware and Lots of real RAm are of little use. My laptop (366mhz w/32mb ram) can render some stuff faster than my desktop (333mhz w/128mb ram). Cas in point: its 99% relted to your CPU.