Hmmmm, GTX 580 about 500 BUCKs, Performance diff for BF 3 Beta 8% in favor of the AMD proc vs the I5-2500k. Cost difference between AMD and a I5-2500k when you look at the whole picture, CPY + MB, Plus a 580 is 6 % lower for an AMD build.
If I was building a new system and the ONLY thing I did was Play BF3 on it, maybe the 50/60 bucks saved might be worth it. But if I'm spending that much, I would shoot for the overall better system - The I5-2500k with a Z68 MB. The CPU is ONLY one part of the equation, the other being the MB and the GPU. As long as the CPU is not holding the GPU back, then either is acceptable. From a MB stand the Intel chipset is better. Unfortunately with AMDs cut back they are having a hard time keeping up with Intel and their vastly larger Workforce and R&D budget to match Intel's driver performance (ie SSD performance).
Then there is the upgrad path, With Intel's IB - TOO EXPENSIVE currently. For AMD there is BD, but I would not call that much of a upgrade.
When looking at the overall picture in terms of 3rd party developement, when designing new hardware/software: If there is a diff in performance between AMD and Intel, quess who is going to win (In General) - the 20 % (AMD) market, or the 70% (Intel) market.