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.