The F250 6.7 has 3.31 gears with 18" wheels and 3.55 gears with the 20" wheels. Both turn about the same RPM due to the difference in tire size and gears balances out. You could get 3.55 gears with the snow plow prep package and that is the best for towing.
Diesel engines combined with six speed transmissions cannot be compared with older gas and diesel trucks. If you think that 3.31 gears are too high, you will really freak when you factor in the fact that fifth gear is overdrive and sixth is over-overdrive.