Its all about pinging. If your bike is doing that then you should stick with 90+.
Now how many new Nomad riders would know a ping from all the other noises coming off these Kawasaki Vtwins ? There's the rub...
Basically, I tell folks if you go with midgrade on a stock bike, and don't lug the engine especially on hot days then you'll be fine. To avoid lugging the engine get in the habit of not upshifting to 4rth till the speedo shows 50+, and again wait until the speedo hits 70+ before going to 5th. And by hot days I mean 80F+...
All that advice assumes a stock bike. If you add a PCIII or other fuel chip and perhaps more open pipes you can get the bike out of that factory lean condition and probably start running regular...