I actually drive a CB300F but the bikes are very similar. I had a bad habit of upshifting at around 4k rpm and did not realize I was lugging the engine or that it was bad for the motorcycle to do this. In fact I was thinking that I am "saving gasoline" by upshifting early and often and was even driving at 35 mph in 6th gear (I did not know there was anything wrong with this) ......Basically I was in the habit to get up to 6th gear as quickly as I could.
I tell you that it is just this week that I started waiting until 5 or 5500rpm to upshift. It still sounds to my ears that I am straining the poor little engine too much by upshifting at 5000 rpm, the engine sounds VERY LOUD if I wait until then. It is probably because I am accustomed to driving a manual transmission car that I upshift at 3000 rpm on the car and have carried over this bad habit to the motorcycle now.
But no way could I wait until 6000 rpm to upshift, that just sounds like the motor is going to blow up, you guys would have a hard time convincing me that 6000 or above rpm in 5th gear is not unhealthy
Generally you are "saving gas" by keeping the revs down and getting into top gear as soon as possible. One thing that also helps though, even though it sounds counter-productive, is accelerating briskly in the range of peak torque (where an engine is most efficient) to get to top gear quickly. That reduces the time accelerating and gets you to top gear quicker.
It's not going to blow! Don't worry about revving as long as you are under the red or even rev limiter. These bikes do get to the track, where they are in the red all day long - and they don't blow.
I'm just concerned that keeping the rev low consistently may lead to excessive carbon build-up. This may be due to poor fuel additives in some countries and not a widespread problem. Good idea to run a fuel system cleaner once per season and rev 'er up now and then!
sendler might chime-in with some mileage tips - he's the Mileage Man!