My iMac is a base model with 8gb RAM, 2.7GHz core i5 and NVIDIA GeForce GT 640M, purchased in Jan 2013. It is still on Mountain Lion. I've recently gotten a 4k video camera, and did some editing on FCP 10. While editing, there were only little choppiness, and the computer handled the entire task very well! The computer lagged while rendering, but it was still useable for other tasks. Furthermore, the fans never went above idle. My iMac is almost 3 years old now, but it seems to become newer computer each time I throw harder work at it! Very impressed. Great job Apple!