Yes, but that's only if you're asking to use ALL of that power. For example, we all have 300+hp pickup trucks these days.Yes....BUT.....
At load...in theory the 60hp tractor will burn 50% more fuel....because it makes 50% more power
However, it only takes a finite amount of power to accomplish a given task. If I'm towing 6000 lbs down the road but I'm not at full throttle, I'm not using all 300+ HP. It's not necessary, the task at hand isn't requiring it all. I saw calculations one time about the amount of horsepower required to move x trailer weight up some specific grade at a specific speed, and it was way less than we would have guessed. It was only like 150 HP.
So, my point, if you were to do the exact same task as the 40 HP tractor with the 60. Same speed, same ground, same implement, obviously the task only requires 40 HP or less. So you're not going to be using all 60 HP. Thus only using 40 HP worth of fuel.
Back to the truck comparison. This is why I get 20 mpg unloaded but 10 mpg towing. While towing the task requires more horsepower. And towing in the mountains even more. And occasionally might have the foot in the floor actually using all 300+ HP and the instantaneous mileage screen shows something like 1 mpg.
At any given time we're only using as much horsepower as we're demanding from the machine. Not necessarily what it has as a maximum. There would be a direct correlation to fuel used at specific horsepower demands.
Obviously this is an oversimplification to try to make it easy to discuss a point, but I believe what I have stated is (at least loosely) true. There are other variables of course.
I would say buy the 60 HP tractor. Running it at partial throttle accomplishes about the same thing fuel wise as them neutering the same engine electronically via tuning.