There's a lot of talk about size of fish in this thread. The photos of the amazing NC trips, with its top notch anglers, also show a number of rods bent to almost 180 degrees.
Other than the quickness with which a large fish can change direction or intentions, the issues are drag and bend, not the size of fish.
The approximate numbers go like this:
30 dgr. bend in rod, load is 50% of drag
60 dgr. bend, load is 100% of drag
90 dgr. bend, load is 140% of drag
180 dgr. bend, load is 200% of drag
The actual drag at any moment (assuming no palming), is what you set times the full spool to actual spool diameter. So if you set the drag to 22 lbs., the fish dove to the bottom in 900' of water, and if the bail was high on the spool (photo below) with line coming off the bottom, the drag could momentarily get to 50 lbs. If you high sticked the rod at this point, the load on the rod would be about 100 lbs. If you "only" bent the rod to 90 degrees, the load would still be about 70 lbs.
I know these numbers are hypothetical but are a good indication of how forces can build in real fishing situations.
Note the 30 degree angle of line coming off the almost empty spool it increases the drag by about 25%.
