My Mac is a Mac Pro 5,1 , quad-core with ATI Radeon HD5770. I use Bootcamp and Windows Xp. CoD performs quite well now, but I'm thinking to upgrade Os to Windows 7, because I've problems with trackIr. After last update of ATI Radeon's driver, TrackIr 5 refuses to load. Apparently it's a known issue, and I'm using my unit in TrackIr 4 mode. On average, Mac computers are tough machines, not directly comparable to Win pc, so, why not use them?
By the way, I use my Mac professionally for graphic and publishing work, and it makes sense to use it also in a secondary role for playing, taking advantage of its excellent quality 27 inches screen.