You know a lot better than to trust a generic snowboard length calculator
While in general I agree that someone 185 lbs would probably be on a 160ish board, but that's a generalization (that also reflect my personal preference
for longer boards). When it gets to specifics, I think he should trust his instincts (he's been riding enough to know his own preferences ... subconsciously at least).
In my opinion, length matters less than construction... if he really wants a board that is more freeride/carve oriented... he need a board that is stiffer and more damp than the Proto (I own a 2012 Proto 154 myself, so I'm not bagging on it... but I know what it designed for an what it can do). Something like an SL or Cobra if you are going to stick with a Never Summer board (I own a 2009 SL 155, haven't tried the Cobra yet).