Are the new iMacs any good for gaming?

My 2009 iMac is due to be upgraded soon.

I was thinking of getting the 27" 3.2GHz iMac and upgrading the GPU to the GTX 680MX and getting the 1TB Fusion drive.

I've noticed a lot of PC games that I'd like to play are getting released for Mac these days (StarCraft 2, Diablo 3, SimCity, Borderland 2 etc).

Anyway, my question is; is it a waste of money speccing out an iMac for gaming, when I can get a comparable PC for cheaper?

Obviously this is subjective, but I just wanna hear peoples thoughts.