I ride a 26 year old K75. Its happy spot starts at 4000-4500 rpm. Its "happiest" spot on the highway seems to be 5500-6000 rpm. It's redlined at 8500 rpm. (I'm told the engine would actually rev a lot higher, if not for the rev-limiter. While I've not done it, I'm told that the bike will run all day long at 7000-8000 rpm and be happier after the experience. I've never done that....and if I did, I'd probably be in considerable legal trouble. There are quite a few of these bikes with 200,000+ and more miles without the engine ever having been touched, but undoubtedly well maintained. The K75 especially is very smooth. Vibration.....just is not an issue.
I came into this world kicking, crying and covered in someone else's blood. I have no problem leaving the same way.