Anyway, to stop the issue from happening on my machine, I manually put my computer to sleep before closing the lid. Simply tap your power button and once the screen is dark, close the lid. I will test this later after playing long enough for my fans to turn on because part of the bug described on apple forums involves under clocking the graphics card after a certain temperature is reached which is later triggered by putting the computer to sleep.
It worked!!! I'm getting full fps for my settings. So, check if this works guys. Manually put your computers to sleep.
I played through act2 hell (fans blazing in the dalghur oasis) and then manually put it to sleep after the fans stopped spinning (approx 13 seconds) and then closed the lid. Just had dinner and opened the machine back up and still have full fps!