Well, the first thing I'd do is check for any dead pixels. Then do a bracket of exposures at 25, 50, 100 and 200 ISO. Start with 10 seconds all the way through 1/125. I'd then do a smaller but similar test tethered to Leaf Capture. Finally, I'd try a series of shots in quick succession to make sure no strange heat-related noise comes up and that the fan is working properly. After that, I'd take it out for a day of casual shooting and make sure everything works fine.
Oh yeah. I'd make sure focus is spot-on with my fastest long lens. Check to make sure the back is seated on the camera body firmly and then test at both near and far distances. Sometimes (extremely rarely) with mfdb's, the shims on the backs can be off a fraction of a fraction of a mm and can throw focus off a bit.