I just measured ground clearance today for my Performance with PUO.I think measuring the ground clearance to three or four spots on the belly pan would be the most accurate method (even if it does involve lay on the ground).
It was 5" at the front jack point and 5.5" at the rear jack point.
P.S. - my jack is too tall to fit - I need one of those low-profile jacks. Thus why I was measuring.