There will be an RPM, according to load and speed, which just feels right. If vibration increases, you could be lugging or over-revving the motor. Play around in the fat spot of the torque curve. Get used to the engine. See where the engine is happy and where it is laboring, i.e. more than half throttle to maintain a legal speed. It has a fairly wide tolerance for revs, but too high is wearing the motor out prematurely, and too low does the same thing, but for different reasons. On level ground at a slow speed, like city streets, I sometimes cruise at 2500 - but am ready to change up or down according to speed and road conditions.
Freeway/Interstate is another creature. I cruise at about 80 per, and that is close to the 7K spike in power that the engine produces. I was trained to drive aggressively and I prefer to work my way through slower traffic and be by myself. Too many close calls with sleepyheads almost running me over. Distance is safety.
Pull up a dyno chart on the motor and see where it begins to produce torque and from there to about 7K, it will be happy. 7K and above, you are getting serious. Mind how much throttle you must give it. If you have to dial it on to keep your speed, it's time to shift down. As well, if you crank the throttle and it does not accelerate, you are most likely at too low an RPM. I guess 4-6K or so is a good general RPM. Too low and that lumpy firing order will stress engine/trans/chain, etc.
You're just going to have to get a feel for the bike, as your roads and riding conditions are different from all others.
1987 EX500-A1<br />K&N/Dynojet kit<br />Webcam 245 cams<br />Cobra F1 slip-ons<br />3rd airbox snorkel<br />Tapered rollers<br />Prog. Springs<br />Russell braided line<br />Galfer pads<br />Avon Super Venoms