Here is a story from my first week on scrapers...
I was running a terex ts14-b at the time and I did my Monday morning routine, started her up and ran after the other scrapers cause I was running a little late that morning. Into the cut I go, the cat picks my up, I fill the bowl and head for the fill area which was downhill from the cut. Get to the fill, unload, and head back up the hill and I have no power, can hardly get up the hill. Again into t eh cut I go, the cat picks my up... to the fill I go. Unload, head up the hill again, still no power. When I get to the top, I start trying to learn why I have no go. The push cat driver tracks by and yells, " You really should try using both motors!"
Sure enough, I was running with only my front motor, basically I was shy about 150 hp or so.
Most of the power in a pan comes from the back motor as the front motor, (in terex) has a hydraulic pump and an air pump robbing power and the back motor doesn't.
That means that on both motors you will get say 30mph, with just the front you might get 10mph. Roading at 10 would take awile.