mmm I don't think so, is not a matter of hardware power, the problem here is the OS in which the game will be released. Basically almost all the games are launch for windows, and some consoles, but only a few for mac, so no.... Mac is probably not your best choice when it comes to gaming.
Rykroft is right. While you can find a fair amount of games on Steam that are compatible with Mac, you will not get the same library of games and support that you will for Windows. Its just not there. If your a heavy gamer, get a Windows PC/laptop.
Yup, the best machine is the one you build yourself.
By the way guys, I had to buy a laptop here in Australia, is not a great thing compared to my desktop rig back in Argentina, but it will do, at least until I settle down an save enough for a gaming machine.