The Intel HD 4000 CPU graphics on the 13" is ranked a dismal 279th place on this chart.
http://www.videocardbenchmark.net/high_end_gpus.html
If you intend to 3D game, you need a Windows 3D gaming tower as occassionally one has to upgrade thier graphics card to keep up with the upgrades and newer games released.
What you got is a Windows gaming laptop, however one can't upgrade the graphics in a laptop. But at least you have extra dedicated graphics for 3D gaming., it's likely you can't play the newer games on it well and your looking for something else, but the 13" is in the wrong direction, it's downgrading your performance.
The 13" has no dedicated graphics what so ever, it's NOT a gaming laptop in fact None of the Mac's really are.
Your stuck with what you buy with a Mac and it might work well for a short time on recent games released or perhaps some older games, but your soon left behind as you cant upgrade the graphics.
Not only that, Apple releases a new OS X version annually, and that slows the machine down and breaks many games.
Some devleopers like Blizzard release new versions only for the last two OS X verisons in circulation, so you upgrade OS X and the game, but it has new features and thus both run slow on your older hardware.
It's because you can't upgrade the graphics on Mac's.
So the only platform you can it Windows and only with a 3D gaming tower.