I remember magazines you to say that several pro's....like Haney, Labrada, Gaspari, Christian, and Ray would stay very lean in the off season.
I think in 1991-92 Dorian Yates, Mike Mattarazzo, Kevin Levrone, and Gary Strydom scared these guys either into retirement, or into being more proactive about gaining size.
Either way, I would say that the average pro goes up to 40lbs over their stage weight duing the off-season