You can shift from low axle to high axle in any gear. In fact that is how we got 8 speeds with a 4 speed transmission and 10 speeds out of a 10 speed. And yes, they will go over 50 MPH. Wind noise, fan noise, and solid lifter noise and no insulation makes them noisy and a lot of people are scared to drive them with all that noise going on. I spent lotsa hours at 60 MPH+ in one of those things 50 years ago.