The 4" will do noticeably better than the old 3". The cowl size (as mentioned above) is the limiting factor.
For underway in hot, steamy places, I'm a greaty fan of fans, strategically placed, for making life below decks better.
Also, for at anchor
where it rains a lot, we made a hatch dodger
that works on the dorade principle, and can leave the hatch
open up to about 25 knots, after that, the wind
blows the bouncing rain drops in, below that, it allows a lot of air in.