You're going to have a hard time breaking a well made rod just from overlining it, even by quite a bit. Your performance should go to crap before the rod breaks. As to heavy tips--it requires more energy to move them. Simple physics. I personally prefer to use as little energy as possible. Most of this discussion is moot. The only common quantifiable factor involved in rod design between the manufacturers is the actual weight of the line it's intended to throw, and even that gets fuzzy with line makers ignoring AFTMA standards. Most rod manufacturers can't even agree on the definition of power and action between themselves. Of the many designers I know, not a one has ever used a word like mass or energy to describe a rod. Many of them still don't even use deflection boards, opting for the "shake and feel" in early design followed up with an actual cast later. The fact that many well respected rod designers prefer lighter tips is merely evident that there is no one true course when it comes to rod design. Why? Because just like rods, we're all built differently. Our muscles respond differently, our brains work different, and even our nether counterweights all weigh in at different amounts. That's the reason a good fly casting instructor doesn't teach everyone the same way--they look at how you're built, how you move the rod, and teach you fly casting in the manner it best fits you. So, as much as I enjoy the mental masturbation olympics, it merely illustrates why so many people look at spey guys like they're clown midgets at a gay pride parade. The human portion of the rod casting equation is a much bigger factor, and quite frankly, none of the fish give a fuck. You can find the right line and rod combo that suits you, but getting dogmatic about it and expecting it to be right for everyone is simply sophomoric.