OP, you're gaming on the wrong platform.
You really have little option to but to suck it up and bootcamp into Windows if gaming is your primary interest; save OSX for getting real work done.
Mac gaming will continue to be several steps behind the PC in terms of reliability, performance and selection for a long time to come.
Sure, I fully expect some of you to be nerd raging at me, but the truth is that only cloud computing will offer the kind of parity that Mac users keep asking for.
That's not the issue though. Many people have stated that their getting great performance on similar or lesser systems. Something else is going wrong with the OP's setup. I'm not disagreeing with you though that PC gaming is far ahead of OS X, but in this case, something else is awry.