Do a simple test under sail on your
boat. Speed when freewheeling vs speed when locked in reverse. It may take 4-5 data points because you are testing with variable
wind speed, but you should get an idea of which is less drag.
If freewheeling is faster and you can put up with the
noise and the wear on your stuffing box and
transmission, go for it. I think
Yanmar advocates freewheeling because their transmissions tend to get stuck in reverse, but velvet drives advocate the opposite because their transmissions don't get proper lubrication when freewheeling.