As Doc said, once at a "cruising" speed, the supercharger is disenguaged unless you try to speed up or go up an incline... So once at 130, it consumes fuel like an N/A. The only thing that would cause slightly less gas mileage, is the fact that the SRT has a 3.07 vs 3.27 gear ratio.

Guess I'll find out in a few months when I move to Germany...