P.P.S. I am running one monitor on the built-in Mini-DisplayPort and a second monitor using the D3100. The laptop build-in display is also running. Depending on load, the CPU usage is between 50-100% of one cpu (out of 4 total). So, the total average cpu load is around 12-25%. Unless you are staring at the performance monitoring tool all day, you will never notice this.