So, ACE ..... are you saying our UCE bullets should cruise at 60 MPH ?
I think it would be a good idea for longevity, although I could stretch it to 65mph, since they seem to be okay there.
If the bike is one of the ones that vibrate severely at 65, then I'd try to work around that, and maybe stay below.
I don't want to be alarmist about it. Obviously some people are doing it, but most engines really are not intended to be run for long periods at near maximum output. It's my "rule of thumb" that I use as 75% of max for longevity, and others might differ.
As a comparison, our Fireballs do 100mph, and we recommend(and have verified) 75mph for long term cruising for several hours. So we do use that across the board for our recommendations.
The Pomeroy Dictum would concur, since that recommends <2500fpm piston speeds for longevity, and that would be around 4200 rpm on the UCE. That's about 65mph with stock gearing, roughly.
So, maybe I'm a touch on the conservative side, but with aircooled stuff at high load near max, it might not be a bad idea to be. Especially in the summer.