I've been driving it at 600 for now. It's a little jumpy, but considering what's running in the background (livewall papers), I could live with it here. OC'ing to 800,1GHz really makes it smooth - though we're almost to the point of splitting hairs, so I'm going to test at 600 a while to try and keep the temps low.
I can slow 0.7.8 down to 250 with setCPU app. Without setCPU app, I'm not sure where 0.7.8 runs at by default.