I have a Mac but don't know much about gaming with crossover except that it's not very reliable.
Honestly, if you want to game on your Mac, acquire Parallels or VMWare and load up Windows XP or Vista in those and see how it works. If you want to use your computer to its fullest, just go with Bootcamp, and boot into Windows when you want to game, that's what I used to do, and trust, me everything will run A LOT better and be easier in the long run.