You will love the 5.38s. I currently run them with 35s. My mileage went up when I switched to 5.38s and 35s from 4.56s and 33s.

Power is great and I can still do 80mph if I have to. I normally keep my cruising at 70 or less. It is nice to be able to accelerate on the freeway again!!

edit > You will still be very comfortable with 37 or 38 inchers too.