I have the same dilemma. I'd prefer to run at about 1900 RPM and my speed is ~ 60 mph. I'm planning on a larger tire and wheel upgrade. I found a tire size calculator via google, entered my current tire and then entered a 19.5" HD truck tire that I'll probably go with. The larger tires an wheels gave me 67mph.
I have a heavy Lance 1161 camper in the bed of my truck and the 19.5" HD truck tire upgrade is a popular mod on the RV sites to help stabilize the ride of RV's by reducing tire overloading and flex.
So for me, it's two birds with one stone.