Thus, in the presence of a 900 vehicle/hour traffic load, having everyone pull over to the right all the time would reduce the safe speed of the road from 73mph to 22mph.
Your given assumptions are flawed. You wouldn't need to slow down again after you passed a slower moving car. You would simply move over in front of him to fill the gap he caused by driving slowly. You would then continue on and outdistance him at a normal rate of speed.
The only way to get back into the right hand lane would be to reduce speed to match the traffic in that lane. And if most of the people are in the right hand lane it will have to be moving pretty slowly. The way to get maximal throughput is to have traffic roughly balanced between the two lanes.