I can get close to 30 on long drives at 70-80 keeping around 2k rpm. When I'm heavy on the pedal I go down big. Like 14 - 16 in a 15 mile playtime.
My daily ride to and from work is about 21-22 15 miles each way Highway. Getting on it when getting on and passing, cruising at a good clip (7AM).
You get really good mileage with your rig, I wonder if the supercharger makes it more efficient even though its more power?