"The answers you want, can only be as good as the questions you ask"
But I'm bored, so I'll guess!
The problem isn't RPM, these will run under redline until Mike Lowreys handlebar clamps wear out. The problem is load, asking an engine to make high HP for long times builds heat.
Running it in the bike for something like the iron-butt nonsense? Sure, I'd do that. Theres much better choices, but I get thats not the point, LOL. The BSFC on a Buell has got to be terrible!
On a road course like a 36 hours of Le-Mans thing? Maybe not.
Hooked up to a pump or generator at full load? NO.
Marine engines live that life, look at what they do, like bearing seats for the valve springs, and you'll know why marine engines are so dang expensive.
Good luck, I'd like to hear more of this mystery question