I'm not wildly impressed by this. A lot of cars can do great fuel economy on a race-prepped track with no real turns (big sweeping corners, not a big hurtle to hold speed), and a slow enough speeds where aerodynamics don't yet play a huge factor. It's a nice marketing stunt, however.
I could get 30mpg in our '98 GMC Jimmy at about 35 mph-40 mph. 4.3L V6 with the 4L60E and all.