Ric:
bring the 4 wt. Really big to me is 48"/40 pounds. Fish in the high 30"/low 40" range haven't developed the girth that makes a cow/trophy. Don't get me wrong; having just put one on ice; a 38" fish is a nice fish, but its not a "holy cow! - look at that!" fish.
The first 40 pound fish I caught was in Bournes Pond and as it came into the light my reaction was "holy s**t". There was a fly fisherman watching me land it and his reaction was "I don't ever want to meet a fish that size with my fly rod".
Once you see a 40 pound fish and feel its heft; you'll know what big really is!