I don't know the rpm but the sweet spot on my 49 1/2 ton 3100 is between 40 - 45 MPH. It sounds good, runs smooth and has plenty of power left for the occasional but rare passing. I've run it up to 65 but only held it there long enough to complete the pass. It lets me know me it doesn't like spinning that fast
Engine is a stock 216 & 3 speed tranny, 4.11 gears and 30" tall (R225-16) tires.
There's an rpm calculator somewhere around here that'll give you the rpm based on some specs you enter.
Good luck
Dave
