Boot Camp doesn't slow down a mac system or run slower than pcs since it's not emulation software. It's basically a separate partition, and a dual boot machine. You either boot into the mac os, or into windows.
That means the macbook pro I use with the ATI x1900 with 256mb of vram runs 3d games and apps at least as fast as any comparable pc laptop, because it is, in effect, a windows pc...
On the other hand, parallels and vmware are emulators (vmware is a bit more highly regarded), and I would just stay the hell away from crossover if I were you...