I think the Sailworks Hucker 4.2 might be just the sail you are looking for if you are sure you are really "detuning" your 5.0 Retro when you start to get overpowered.
If so, the "wider than normal tuning range of the Hucker 4.2 should cover any conditions between your 5.0 Retro and a 4.0 Revo.
Another option (with a bit less overall range) would be a 4.5 m2 Retro, or a 4.6 m2 Revo.
These 2 won't tune down as far as the 4.2 Hucker, but if you are only going up to 25 knots or so (for sure < 30) then they might work well for you.
Water temp in the sound is pretty warm, but as always, it depends on what fronts are coming through.
I've sailed in Mysterioso shorts and a neo rash guard once this year.
The reports I'm getting is that the temps in the Pamlico Sound are 60 deg. F or higher.
Hope this helps,