I had the random thought that I'd like to see the range vs time chart for a Mk16 DDM to see at what ranges each of the 4 possible flight profiles was best for minimal time to target.
The 4 profiles of course are whether each of the two drives is set to high or low: low/low, low/high, high/low, high/high (with the appropriate ballistic interval inserted as necessary).
I plotted out the time to range for each of these from 6 to 30 million km as can been seen here

Up to just under 8 million km high/high wins.
Between 8 and 22 million km high/low wins.
Past 22 million km low/low wins.
Low/high does edge past high/low past 28 million km, but by that point low/low has them both soundly beaten.