Blender viewport and UI lag when external monitor connected I have a macbook pro running windows 7 and I use a 1080p monitor when at home with laptop screen disabled. When I have my second monitor plugged in (via mini display port -> VGA apple adaptor) there is a lot of UI lag.

Nvidia 650M GT oc'd

i7 quad core hyper threaded 2.7 -> 3.6GHz

8 GB RAM
Turbo boost (3,6GHz) only boosts one core. The others sleep, I guess.
So I guess you shouldn't use the boost here. RAM is okay, unless rendering, graphics card isn't used anyway. I use mini-display-port on my System as well, no problem. But im on windows so maybe it's a MAC's problem. Please check out other programs, like Video editing Programs or other comples ones like photoshop. (there are free trials)