so if the tractor engine cannot produce much power at low rpm, then it will have to run faster to power the machine.Err they are designed to make full power at low rpms.
Tractor engine not so much
At the end of the day, Power = force x velocity. So to shift a machine at 60km/hr will use a specific amount of power. Whatever engine speed this power is generated at, the requirement is the same.
The efficency of the engine will vary with speed somewhat but if its powering along at 60km/hr at 1000rpm, the fuel consumption will not be a significantly (depending on the definition of significantly but im 25%) different than at 1500rpm.
Fendt, nor their drivers cannot change physics im afraid.