First of all, the Allis has more drawbar horsepower. This is a function of tractor weight (heavier tractors deliver less horsepower to the drawbar) and the amount of horsepower the engine can deliver. I don't think the John Deere or Oliver are in the same class as a '45, though. The Allis is rated at 43 hp, I believe, and I doubt these other two tractors deliver much over 30 hp. Another factor is the mounted plow. Mounted plows are usually more efficient than trailer plows.