It really depends of the total amount of kinetic energy being lost as the blades engage the grass. The energy loss is a product (literally a multiplication product) of two things: the sharpness of the blades (in this case an inverse of sharpness, e.g dullness) and the resistance of the grass.
I always run the tractor at full throttle. The range that you are in is not a factor when cutting grass like it is when you are plowing. If I am plowing in duripan with the subsoiler, I cannot even move in high range because the torque is too low. In low gear, with higher torque, I can move.
Rather than which range, the actual speed is what matters. The faster your velocity, the more grass there is that enters the deck in a given time. Each rotation of the blade must cut a greater volume of grass and expel or mulch it. In sparce grass that only needs a slight trim, I can cut at full speed in high range. If I have waited too long and the grass is both thick and tall, I have to creep in low range or risk stalling. In either case I want the throttle at full so that the blades are spinning at the highest possible RPM. The blade speed is completely independent from the range that the drive system is in, and the torque to the drive wheels is not as significant of a factor as when plowing. Obviously, when all other factors are the same, a larger deck is cutting more grass per unit of time, and is therefore experiencing greater resistance. This can be compensated for by reducing speed such that the volume entering the deck is equal, as is the area in square units that is being cut. Also, more total energy is being lost to gravitational resistance when traveling uphill as opposed to downhill. In a couple of steep locations, while brush hogging, I cut only while traveling downhill. I do not cut as I return to the uphill location for another pass.
The other factor, blade sharpness, speaks for itself. Far less energy is absorbed by the grass stems when a sharp blade slices through them, as contrasted with a dull blade ripping the plant tissues apart.
Ideally, you want max sharpness multiplied by max RPM of the blades. The variable is the forward velocity of the tractor. Regardless of range, the maximum forward velocity should be the speed at which you do not lug down from resistance in the MMM deck, AND you get the cut quality that satisfies you on the lawn surface. It is possible to cruise at a speed at which there is no lugging, yet the cut is not as clean as it would be at a slower velocity.
The greater weight of the tractor will not be a factor as the greater hp more than offsets that. The greater number of cylinders any recirocating IC engine has, (assuming bore and stroke, fuel, all other factors, etc. stay the same) the better the torque. In a 4 stroke engine, the crankshaft rotates 720 degrees between the time one cylinder fires and the time that it fires again. In a 2 cylinder engine, the crankshaft has to turn a full 360 degrees so that the first cylinder is beginning its intake stroke as the second cylinder begins its power stroke. After the power stroke, everything depends upon the internal inertia for the first piston to complete its exhaust stroke while the second is making its compression stroke. In a 12 cylinder engine, the crankshaft has moved only 60 degrees following one power stroke, before there is another power stroke. There is always pressure from at least two cylinders and power is not petering out. In a three cylinder engine, the crankshaft has to travel 240 degrees from power stroke to power stroke. In comparable engines with differing numbers of pistons, the greater the number of pistons, the more smoothly and constantly is the energy applied to the crank and drive shafts. Therefore, the three cylinder engine is more efficient than the two cylinder engine.
Hope this helps. Good luck!!
