From what knowledge I've gained from this forum, it appears that 5-7K RPMs represents the most efficient range for transmitting power and accelerating. As such, shifting in this band is preferable -- the upper part of the band or beyond when max acceleration is desired, and the lower part or even down to 4500 RPMs when in a gentle commuting mode.
I have read that shifting at too low of an RPM, say below 4000 RPMs is not desired, as the engine is likely to lug along, which is not good for the engine bearings.
My first day out with my bike, I was lugging a lot, shifting at 2500-3000 RPMS to get used to the manual transmission. In hindsight, boy was that engine lugging back then!
When you feel the bike stutter like its having an epileptic fit its probably time to bang up a gear.
When it's not going any faster its time to bang it down a cog.
problem with the cbr its got a narrow band between 8500 and 10,000, outside of that it moves slower than Australia Post.
Common internet advice: Something is obviously wrong with the bike. Tear it apart. Buy new stuff. Throw money at it instead of fix the cause.