4.10's
The numbers on the web-site are pretty accurate. I just changed from 3. 54's to 4. 10's because of the loads I pull, and difficulty maintaining speed up the hill.
This weekend my Dodge did it's first trip pulling the 13,000 LB fully laden toybox over the hills to the dunes at the coast.
What I found was that at 62 MPH I was turning 2000 RPM. The engine really "likes" that RPM and pulled the trailer with ease. Up the small hills (+/- 3%) I could stay in OD and pull the hills in fourth and maintain 60 MPH. The 4% grades required third gear and was able to run 45-50 MPH turning 2500-2800 RPM.
My hill climbing speeds have improved by 5 to 10 MPH because I no longer have to drop into second. Fuel economy is about the same, about 11 MPH. It would be better, but my run is constant up and down, slow down for corners, then speed up. Not the most economical driving conditions.
My fifth wheel stands 13 ft high and is 34' long so it catches lots of wind. Wind drag can make a big difference in towing performance.
I am very happy with my new 4. 10's. I miss the unladen cruising speed of the 3. 54's, but for me the trade off is worth it.