It was or still is the best GPU in that TDP class. It is obviously not a desktop GPU. Those are allowed to suck 150W+ and are obviously a different league.
It is just as good as any other 650M in other notebooks. Like the Asus UX51VZ or Samsung Series 7 (the new one has a 8870M which is slightly ahead).
If you want more performance play in Windows (bootcamp). Apple writes there own drivers and they simply do not come with all the DirectX optimizations for even individual games that exist in Windows. Games on the Windows side simply get more attention in every possible way.
Personally I think in Starcraft 2 the difference between low and med is huge. Yet everything past medium makes very little difference. I would just crank up the res to the highest that works GUI wise. Set most settings to medium/high. Add AA/AF. If there is still room raise the settings a bit more.
Resolution first. AA second. The rest imo doesn't really need to be any higher than medium/high.
A game engine always picks its own resolution. It doesn't give a rats ass what res you have set in OSX.
If you want comparisons to other GPUS out there.
http://www.notebookcheck.net/Computer-Games-on-Laptop-Graphic-Cards.13849.0.html
In general though you need a real gaming notebook like all the Clevo to get significantly more performance or wait for the next gen.
The coming next gen is mostly just better auto over clocking. Nothing you cannot do yourself in Windows with the laptopvideo2go drivers and some profiles. 20nm serious next gen with an actual big performance increase will show next year. That is when you can start complaining about to little performance compared to current top of the line.
If you complain now get a desktop. Much cheaper much faster. In a desktop you can exchange for 200 bucks the GPU after 2 years and it will again blow every 2000$ notebook out of the water in performance.