I have been shifting based on how the engine sounds but it also depends on my mood. I usually shift between 2500 and 3500 rpm.It is not that simple.
A zillion variables come to mind including what mood I’m in. But things like the road incline and just what my intentions are for the next shifts.
And that’s the fun.
I go by ear, not the rev counter. If the drivetrain starts sounding scary, upshift. If it starts lugging down, downshift.
Repeat for years on all terrains and weathers. Happy motoring…
Learned manual on a civic with no tach. Even with my Audi I don't pay attention to the tach. You feel the ideal shift point overtime for your driving style and environment. Just don't bog it or ride the rev limiter.This is how old people talk, apologies.