I have the same car/combination (essentially). I have to side with Bullitt, although I understand and won't completely trust the onboard computer (which reads around 29-27 mpg on cruise.) It just sips fuel when I'm not stepping into it.
That said, probably because of exhaust flow (no cats, straight out), the car is effortless at 70mph.
The new math: Having my cake and eating it, too.
Coop