Makes absolutely no difference on the gearcase at the speeds we can reach. Now on a prop where the tip speeds well exceed those 100 mph velocities of a gearcase in the water, there is some consideration to be given to finish. If you check with your premium prop builders and tuners (such as Throttle-Up) I think that you will find that even on the polished, show pieces, that the leading edge is "scuffed" or sanded to allow a better flow of water and to reduce the effect of surface tension drag. Bottom line here: A satin (or natural) finish is potentially slicker at super high speeds but most of us won't notice the difference at the speeds we run so we might as well finish that lower unit the way we think it looks good. --- Jer