Great Harbour N-37 and N-47, late model Selene 36, Krogen 39 are "walk in". Full "stand up" head room is only first four feet in KK 39, Great Harbour N-47 is full standing, N-37 is maybe 5.5' or so, Selene is probably near 5'. Other custom one-off builds occasionally, older 44' DeFevers, Matthews and 43 & 44 Gulfstars are pretty good too. Maybe Nordhavn 43 & 47 but I haven't been in either. That's all I can think of under 50.
Any DeFever over 44' is very good for ER space and height. Much better than a KK, Selene or Nordhavn of similar size. I was on a Nordhavn 50 yesterday and was noting the lesser maintenance access.
But, with good planning and long arms anything has been shown doable on these nice vessels.
JP - I'm pleased and amazed at the size in your boat's engine room.
Designer of that gets double -
Lou Codega designed those boats.