Good question...
I'm guessing the difference would be minimal. On the Moeslyseacraft.com site Carla had some Mercury tests for the Bowrider and the 20' but they were like 125 O/B vs 140 I/O and a 100 O/B vs a 120 I/O.
In each case the greater HP I/O had advantage ranging from 1 to 2.5 mph top end... I guess you could extrapolate from that or just gather some of your southland buddies and go get some answers for us
