Not necessarily. The higher HP ones drink more fuel, among other things. Farmers are not always looking for "more power!"... they want the right amount of power for the tasks at hand. If the lower hp tractor gets the job done and saves a few gallons per hour of fuel, that's money to the farmer's bottom line, right? Farming is a penny-pinching occupation!
Yes....BUT.....Correct me if I'm wrong, but there is a somewhat direct relationship between the amount of fuel and air required to make "X" amount of horsepower. Timing and some other things can affect that obviously, but there is at least a rough correlation.
So, I wonder how fair it is to say a 60 HP tractor is going to burn more fuel than a 40 HP tractor would while doing the same job.
If it's doing a job that only requires 30 or 40 horsepower, unless you just have the tractor pegged out for no apparent reason, it's only going to consume 40 HP worth of fuel, because that's all that's being demanded of it.
So, if you're only using 40 HP from your tractor that's capable and tuned for 60hp, is it not going to use about the same amount of fuel as the 40 HP tractor giving you 40 horses.