I know my dashboard (ZomB) is similar in speed to what you were getting. Although I did not have a CPU or FPS indicator, I had about 5 other controls on the dashboard, and at one point I looked down at the image, realized that our camera was pointed at us, and waved, and watched my hand in real time. (We got tipped on our side, video here:
http://thecatattack.org/media/view/2596 (I wave at 1:25 and at the end) )
I had actually been noticing an interesting delay that eventually built up between reboots, that caused the UI of the DS and DB to lag by about 3-4 seconds to respond to mouse events after 6 hours of restarting the DS and DB (clearing FMS Locked), and was surprised that the video was still not laggy.
I would think the difference between DirectX, IMAQ, GDI/GDI+, and WPF is negligible unless some other process is hogging CPU (like many charts)