When I click the Apple logo in the top left -> About This Mac -> more info... I see:
Graphics Intel HD Graphics 4000 1024 MB
But I bought it with nVidia GT 650m graphics. So I click the Displays tab and again it shows Intel HD Graphics 4000. So I then go back to the Overview tab and click System Report... -> Graphics/Displays. Intel HD Graphics 4000 is highlighted, but below it I finally see the NVIDIA GeForce GT 650M!
Is my system using Intel HD Graphics 4000 instead of the more powerful GT 650M graphics? The machine has been amazing, but Unreal Engine 4 is a bit slow.