Why waste so much money on a mac, macs aren't designed for gaming. Buy a cheaper PC or build your own computer.
Why do you guys always want to get in people's business/personal space, if he wants a Mac let him have a mac, accept his choice of computer and just answer his question. You should suggest to him that maybe getting a gaming PC would be "better" not demand that he gets one.
(And the whole macs aren't designed for gaming? There's really no "requirement" for a computer to work for gaming, Linx isn't designed for gaming and can it play games WHAAAT)
@OP, currently shaders on Mac causes some weird lines on the entire screen, the highest setting you can go without everythig looking broken is minimum. Probably the only way to fix this right now is that you can install windows on your Mac and have both the Windows OS and the Mac OS. You need a windows installation cd and a Mac installation cd/USB.