I was thinking about this too since I consistenly get in the very high 30's and low 40s where my husband usually gets more like the mid-30's. I try to keep the RPMs right around 3000 and he tends to prefer 4000. So I shift a lot, trying to keep that 3000. The only time I can't keep it there is high speeds (highway trips), and that's when I get lower mileage.