I’ve always thought that without changing out the transmission to gain an overdrive or something else to keep the rpms down, it seems like a 3.31 or other higher-ratio axle would make your "highway cruising" uncomfortable/loud. when I get around to the "posi" rear, I’ll be staying as close to 2.88 as I can (just my thoughts). A big factor would seem to be your intended use of the car.

Good luck with whatever you decide.