Thanks everyone for your replies. Jeff, thanks for the table--lots of good information! I think ground clearance comes closest but is not it. Someone on 6speedonline pointed out to me that ride height is a fixed measurement from the ground to some predetermined point/bolt on the chassis. Similar idea to this particular post:
http://forums.rennlist.com/rennforums/showpost.php?p=3994733&postcount=2

Some interesting info; notice the huge 40mm difference in front between 996 Turbo and GT2:

996 Data

* USA Turbo
Front 148mm to 168mm
Rear 148mm to 168mm
* ROW Turbo
Front 128mm to 148mm
Rear 138mm to 158mm
* GT2
Front 108mm to 118mm
Rear 133mm to 143mm

When I saw a 997 GT2 a few weeks ago, I did measure the mid-fender heights of that car against my 997 Turbo out of curiosity. To my surprise, this method did not show that big of a difference, an indication that fender heights do not reflect true ride heights.

Turbo:
LF 67.6 RF 67.1
LR 69.0 RR 68.7

GT2 (was NOT on a level spot, best that I could do)
LF 66.5 RF 67.2
LR 68 RR 69.5

I now am just curious if the difference between 997 GT2 and Turbo is as big as 996 GT2 and Turbo.