Hardest thing about gaffing, is to not swing the gaff at the fish... we always netted under about 20 lbs, gaffed up to 40, and harpooned over 40... The first thing to check when you can see the fish, is how well is it hooked. If I could not see the barb through and through, I would reach for the harpoon if it was any size of keeper... I only shot two fish during my Alaska years, but the largest I personally boated (125 lbs) was just a harpooned/gaff job. It was too rough to even consider gunplay that day.
