Well surf fishing with 3" baits on 3/16oz leadheads is much different than fishing 5" baits with 3/4oz leadheads in 60ft of water. I wouldn't drop below 12lb fishing 4 and 5" baits from a boat. 15 and 20 is much wiser. The bigger baits require a harder hookset because of the size of the lure, and you also have more line out so line stretch is a bigger factor, not to mention the fact that you can't chase fish that you catch, and half the time you're pulling them out of rocks and kelp. You don't have half of those problems surf fishing or float tubing so you can use lighter line. I use 10lb sometimes for 4 and 5" but I'm sure one day I'll get burned.
-Brian