Sorry but that makes no sense! Lines are rated in "test" which is a reflection of the load they can bear up until failure. While some lines like Ultragreen are underrated, in gerneral, 30 lb line (regardless of wether its mono or braid) has a 30lb breaking strain. If line broke at 50lbs thenit would be called 50lb. Additionally knots NEVER perform better than the actual strength of the line so I would say that unless a manufacturer is totally mislabeling their lines, you cant take 30lb power pro, tie a knot in it and get 50lb breaking strain.
BTW fishing 65 -80 lb braid on the fraser means that if you snag your weight or your 25lb leader, your main line doesnt snap leaving lengths of braid on the river bottom.
One of the reasons that braid has a higher breaking strength than mono does is because more, smaller filaments
braided together yields a cumulative fiber with a higher breaking strength, yet smaller diameter. When mono is stretched, because it is a continuous single fiber, the pressure is exerted on a small section. The way in which mono breaks could be likened to tearing duct tape, in that once the fiber has begun to tear, it tears quite easily. Not so with braided line. The multiple fibers that make up the braid itself provide additional tensile strength.
As well, the lack of stretch that braid provides is extremely beneficial to the longevity of the line. Stretch, for a number of reasons, is mono's biggest downside (at least in my opinion) because it puts stress on the line, and as a result the line is more likely to break in a section that has undergone previous stress. The "stretch-free" aspect that is a big selling-point for braided lines is nice not only for feel, but for strength as well.
As well, line "test" is somewhat of an irrelevant measure as it applies to size of fish. Over the years, those that have used various brands, compositions and styles of fishing line have no doubt noticed that some are just inherently stronger than other fishing lines. This is due in part to material, quality of manufacturer, quality control and just plain luck, but also due to the fact that there is no industry standard. As you mentioned Gooey, Ultragreen is stronger than marked in a great number of cases, and fish well in excess of the stated line "test" have been landed on Ultragreen, as have quality lines like Platypus! However, fish do not exert an instant, consistent mass/stress on the fishing line. It fluctuates, due in part to the movements of the fish, but also due to the millions of variables involving water conditions, fishing rod, reel, mineral content etc...there are too many to name!! I, for one, do not believe that "test" is a uniform, true-to-size unit.
-John