The overdrive would be nice. When I switched to 37s on the stock gearing (for a week) the truck had plenty of power. After I regeared it, I was just like you 70-72 cruising and didn't want the RPM to go any higher. Unfortunantly, I have no experience with the roverdrive unit. I was going to swap in a 1.22 unit and get the reduction that way. The 1.4's are worth a little more money so it is a free option. Never did it though, and now I have 6.20 in the diff
so I max out at around 55 mph. Good luck.