HERE IS THE BOAT SPECI couldn't find info for the 2010 (or similar) 390DA with sterndrives - my books were missing that data. But here is a model that is very close in dimensions/weight and at least gives us a good comparison. This is a 2012 370DA. Top speed is about 13% higher with sterndrives - while not the most important thing to look at, this should equate to a higher cruising speed, as well - and, actually, might show a higher % increase in cruising speed.
CRUISE SPEED OF 45 MPH @ 3900 RPM
HERE IS A VIDEO OF THE BOAT RUNNING GO TO YOUTUBE AND TYPE IN THIS BELOW
38 Fountain Express Cruiser Sea Trial Twin 320 HP Cummins Diesels
LOA 37 ft. 11 in.BEAM 10 ft. 6 in.
DRAFT 3 ft. 2 in.
WEIGHT 13,500 lb. (dry)
DEADRISE 22 deg.
FUEL 270 gal.