If you search for "Kubota [enter model here] Bid Specifications" you can typically find far more detailed specs published from Kubota. The dealer can also print these out for you, they are several pages long. One spec they include is "gallons per hour at PTO speed." I was considering an M6060 vs the MX6000. Engine HP and PTO HP were fairly similar but they were very different engines...the MX had the venerable V2403 2.4L turbo 4 cylinder and the M6060 had the equally venerable 3.3L turbo 4 cylinder. The M6060 is quite a bit more substantial than the MX, with heavier duty basically everything. Whereas the 2.4L turbo is basically maxed out for power, the 3.3L in the M6060 is near its lowest power output. The larger displacement produces quite a bit more torque, and allows the engine RPM to peak lower. There is also the 540e option on the M6060 for even lower RPM operation. When it was all said and done, I went with the MX6000 because for my delicate flail mowing operation on very steep slopes, I wanted the precise control of HST which is not offered on the M6060.
Regarding turbo fuel consumption, the purpose of the turbo is to allow a smaller engine to make more power than it would otherwise. This is done by packing more air into the cylinders because the turbocharger is pressurizing the air. In turn, this allows the injectors to push more fuel into the cylinders and the resultant combustion explosion is more forceful than it would be under natural aspiration and lower fuel volume. Keep in mind, these are completely modern electronically controlled engines. Pushing more fuel without the added air simply means unburnt fuel which creates soot and wastes fuel. Sensors detect air mass or pressure and send that info to the ECU, which can also calculate load and take input from other sensors to determine how much fuel to inject. These engines use cooled EGR recirculation, and I would assume they do in fact have a throttle plate which is controlled by the ECU to vary the amount of EGR / fresh air mix.
Regarding the reliability of the turbo and ease of repair: at least on the 2.4L engine, the turbo is tiny, easily accessible, and is not intercooled. Instead of the exhaust manifold sending end gases straight to the DPF, it sends them through the hot side turbocharger turbine first, then to the DPF. Spinning the hot side turbine simultaneously via a shaft spins the cold side turbine, which draws air in from the air filter, pressurizes it via the spinning turbine, and discharges it via ducting into the intake manifold on the engine where the charged air is distributed to the cylinders. The turbos are lubricated by engine oil - I haven't looked to see if they are also cooled by coolant. I'm guessing just oil based upon their small size. The worst stress the turbo will suffer is during an active regeneration where excess fuel is sent down the exhaust manifold and through the turbocharger into the DPF. As far as reliability, you can't work on a modern naturally aspirated engine either in terms of the electronics. The NA engine pretty much has all the same sensors and inputs and outputs from the ECU to run the engine. And regarding turbo engine reliability in general, keep in mind all your long haul 18 wheelers, 10-wheeler dump trucks, trash trucks, snow plows, diesel pickups, large construction equipment, etc etc...all use turbos and many of these things go to a million miles or more. Most people don't know, but even these small Kubota diesel engines are built like a heavy truck engine. There is no timing chain or belt - they are direct gear drive for the camshaft, etc. The block and heads are iron - not aluminum. The crankshaft, pistons, valvetrain are all exceptionally heavy duty. I have no concern as to the longevity of my 60HP 2.4L. Somebody was mentioning what likely was the Ford EcoBoost twin turbo V6 engines...those are far lighter duty engines than these Kubota motors. Even the big HD diesel pickup engines are all using aluminum heads (except Cummins).
Conclusion for the OP: The smaller turbo engine will probably use more fuel under PTO speed than the larger NA engine. However, for everything else like transport, loader work, idling...the smaller turbo engine will use less fuel. Keep in mind the larger engined tractor is also a heavier machine, which means more power is used just to move the tractor itself, which also burns more fuel. Kubota HST transmissions are probably the most efficient in the industry and better quality than most. The gear drive shuttles are excellent as well and deliver a little more HP to the PTO.
