Stop listening to people telling you to clean cookies, I know 100% why your laptop is doing this, i'm fighting apple right now to fix it.
One word. THROTTLING.
If you run a tempature program you'll see the following, when you do you'll know Mittwaffen was correct.
You need to run SC2 on max everything, it'll run like crap but keep up an FPS meter.
Your temps will spike to 95+c, when this happens your chip will slowly throttle (Mine throttles to 800 mhz!!!).
When this happens you will see your FPS slowly decrease as your chip throttles down slower and slower.
Your MBP doesnt have proper cooling, becuase apple rushed 2011 MBP design and look...we have issues.
Feels good to buy a 2000+ dollar laptop that runs at 800mhz when you actually need the speed eh?
Go the the apple store and show them this thread. They can contact me because I have stacks of research that have proved this as a solid FACT.
Show them this, then when they lie and say it doesnt you can run the test for them.
Apple cut corners, and now we get ripped off and flasely advertised (2.4 more like 0.8ghz on load).