Well that's me proved well and truly wrong then......
How about going for something smaller that can still do the salty stuff and get under the bridges when needed for the best of both worlds, my 30DS with twin 150hp's does pretty well and still gets under most of the bridges (except PH,wroxham,wayford, beccles old) which leaves plenty of inland cruising for when the weather is bad but will cruise at a comfy 16knots when the wind is kind, southwold is only 1.25 hours from yarmouth mouth, and 4.5 hours will get you from southwold to ramsgate, 3.5 hours to wells.
Salty sea dog and ditch crawling all in one package.