The reason to vary the speed is to develop a wide wear pattern on gear mating surfaces. That helps to avoid gear noise. Do not set the speed control and let it go for long periods of time before 1,000 miles. If you are going on a long trip, take some county roads at 45 MPH
to mix it up with the 55-65 MPH
I would leave the factory fill oil in for 2-3,000 miles to ensure that the rings have seated properly.