If you have a good boat driver, he/she shoiulf be able to get you on top of the fish regardless oif your tackle, and then you have to work a bit. With anything over 100#, a 15 wt is a help but not essent6ial. Just point your rod at the fish and crank the reel. It doesn't feel too elegant, but works well, and the stretch in the fly line will keep you from breaking off. Keep as myuch bend in the rod as you feel is safe, but just keep crankiong the reel.
Listen to Josko re: fighting fish.
I read an article on Florida Sportsman, "Take It to the Limit, Shorten battles like a fly tournament champion, By Terry Gibson" Which discusses the system Andy Mills uses to determine the capabilities of his gear.
Regardless of what you think of Andy Mills, the guy C&R BIG fish and this is some good info - at least food for thought.
Personally I'm sick of seeing photos of stressed out exhausted fish from being landed on too light fly gear.
Just my $.02