Yep, even flying through the Jade Forest I can hit 80% CPU utilization, even though my GPU doesn't usually get over 60% even in busy areas. I have my settings mostly the same as you do. Did you do any overclocking on the 4630k, or is that at stock speeds? I think if I were to get an IB-E mainboard it would probably be either the intel one or the asus one. Whichever is the most reliable.

Actually I have been experimenting with ISBoxer over the weekend too. Strangely it seems that my FPS is quite a bit lower vs. using Hotkeynet. I think it must have something to do with how it scales the windows down from the higher resolution to the smaller resolution.