Those of you in the know have the private info that I built the flashes on 89 octane. That's all my bike runs. So why do I suggest premium, and not support using regular? Simple. I know that 89 is sufficient as long as my bike isn't being exposed to some crazy ambient heat, and the bike isn't running on the edge of overheating. But i know some stuff, like mitigating cylinder pressure in the heat by not trying to do repeated WOT runs. Some folks don't know that stuff. So I err on the side of caution by advising to run premium, same as kawasaki.
Think about it... a tank of fuel might cost 3.00 more. 100 tanks might cost 300.00 more. Eat the pistons, or thin the oil to the point bearings touch the crank, and it's going to be alot more than 300.00.
I'm really down on the 87 idea because I have not tested it. I don't know where the point is that 87 octane is insufficient. I don't want to find it, and I don't want YOU to find it either. I can hear it now "the flash caused it". Sure. It wasn't the insuffient octane, right? So OK, everyone can do themselves. Just be sure you fully understand the consequences when you make that choice. Kawasaki says a min of 90 octane. You bought the bike knowing that, and won't go wrong with that advise. Pay your money, take your chances.
Oh, ans FAIS... 89 octane is midgrade, not regular, which is generally 87 octane.