There's no more fatigue at any RPM if you can't feel it.
If your bike vibrates fix it. Or buy a better one. If you don't like the sound listen to a formula one or Moto GP race before you ride. I can't stand lugging any engine, especially a short stroke pisswinder like I usually ride.
Almost all motorcycle engines are designed for near max power from a given displacement, because that's what makes the moto magazine writers happy. To do this the cams, compression ratios, intake tracts, exhausts, valves and a hundred other perameters are all engineered to work together at this higher RPM. The more high performance the engine is the more this is true. To run them around like a John Deere does them no good. The bikes are designed to have the engines spun at a high RPM, they are most efficient at the RPMs they were designed to run. They last longer spinning at an appropriate RPM, they burn less fuel, they stay cooler, it's all good. I have never seen a bike which actually benefitted from taller that original gearing. Usually they become dogs, slow off the line, too far between gears, and you end up spending more time in the lower gears because the top gears no longer pull the load.
Now you don't like it anymore, so you go buy a bigger motorcycle, and the story repeats itself.
If you guys don't like the sound of your engines buy an econobox or a minivan or something.