I am not sure how useful this will be for the subject of this thread, but here it goes. The Triumph is a twin with four main bearing journals and counter balancers. There are two firing orders for these bikes, 360 degrees and 270 degrees. The engines with 270 degree cranks are much smoother on the street than the ones with 360 degree cranks. The race part suppliers have figured out the proper combinations of piston weight, connecting rod weight, and crank balance factors for the 360 degree engines. I would need to figure everything out on my own if I use a goofy firing order. With a 360 degree crank I am building on their experience.
The target rpm for my engine is around 7,500 rpm. I gear for that. There is always the possibility of a tailwind or me putting on too big a rear sprocket. The engine is built to run safely at higher rpm if this happens. Bearing shells are on the loose side of tolerance. The oil hole edges on the journals are chamfered. Carillo rods. The gudgeon pins are offset 1 mm in forged racing pistons.
These engines can be built to run over 9,000 rpm. This advice was given to me if I planned to do this. Polish the crank and grind knife edges on the webs, enlarge the oil passages, and rebalance the crank for high rpm. They told me the balance factor. Also, I was advised to use a metal treatment that is also used on F1 car engines. I did not do any of the things in this paragraph. I would only go up to 9,000 rpm accidentally, or never.
It sure made sense to me to trust the experts on the issues associated with high rpm. I am a low dollar guy and a crank break would set the program back. Besides, that exploding motor would be right up close to a sensitive part of my anatomy.