My 57/235/4.10 half tonner would do 65, even 70, but it was really pushing it to do it. 60 was much more comfortable. That was with 235/75/15 tires, about 28" tall.
My current 55.2 has a 235 with 3.54 gears and is much happier cruising 65. With the granny 1st, it still has all the gear I can use. Haven't checked mileage due to irregular use, but I'm guessing it's somewhere around 10-12.
Devin
