the idea of a large enuff rod to do the job needs to be ratcheted up size/weight wise. If you're gonna go for large fish, have a stick that'll fight hard, fast (IMO, YMMV). Shoot for a 8' or 8'3" 15 or more, 'cuz you're really not creating a 'casting' problem; these fish have been known to be fought to the point of exhaustion, released and then have turned up as floaters. My heaviest rod is a 14 and I'm not sure I'd want to go after a giant unless I planned to do all the work with the lower third/butt end and a diesel engine powered reel.
Not that it needs to be repeated, but don't forget to make a weak link in the system, either.