For me personally... . right now with 3. 73's I'm at 1800rpm @ 70mph in 0D, depending how heavy I am, and how hard of a pull I'm into, I can shift down into drive and still maintain 70mph at around 2000rpm, not going to do that with 4. 10's.
My truck gets fairly good and consistent mileage as long as I keep under 2000rpm, go over that and mileage is out the window. Plus, I do not like running my truck at 2200rpm+ for prolonged periods, even though that might be in the "meat" of the power band. That's just my preference, not implying anything wrong with that driving style, just not mine.
On a side note, when I was driving with/for my Dad, with his 220's, 250's, and 335 Cummins, he wanted you at 2250rpm as much as possible. Later with the 350/400's/450KT, Cummins changed fuel timing/duration and torque curve dropped, we were rattling down the road between 1600/1900rpm. I stopped driving for a living in 1992, quite a few changes since then also.