re: 21 ft Bass Boat with 350 HP? WTF

Only boat that comes to mind that can fully exercise the benefit of a 350 or 400 Verado is Bass Cats Jaguar. Boat is huge and loaded weighs a ton, but that hull design will let that big ol bitch get up and talk. Good set up and driver can have two fisherman, gear and normal fishing weighted Jag running 83-85 mph.
Of course if you REALLY want to fly you scale the boat back to a 19-20 fter like an Allison, Bullet or Stroker and put a racing 300 X on it. Smaller lower unit, more hydrodynamically designed and won't blow out if set up well. I've been in an Allison 2002 with a worked 150XR2 that would do 87, a Bullet with a 300 X (non-stock) that did 96 and a Stroker with a racing Merc that did 101.
Fun as hell but the pucker factor at those speeds can make a diamond out of a lump of coal.
FWIW I would never have done that in any of those boats if I did not have good knowledge of the drivers and their abilities. One wrong move and it's "See Ya".