90mph x 6HRS = 540miles / 15GAL fillup = 36MPG

I don't think a Prius would do much better at that speed.




In all honesty, I'll bet the Crossfire would actually love running at 90mph for an extended period. And for the record, I think my old Miata was pulling more like 4,000rpm at 90mph and it never skipped a beat.