well...this question hasnt been asked many times, but it has been asked..im not going to say to search, thats not what im getting at. but i dont know if anybody really knows. i believe there are some charts floating around with a general idea, but for the most part i just shift a little before redline and im fine
I don't know the answer either but I generally find changing up at about 7600-7700 is about right for me.
I suppsoe it depends on your gear ratios as well.
For getting off the line I experimented on the drag strip for a while and my quickest starts are with 6500 rpm, anything higher and I waste too much time wheel spinning. But that is with button clutch so it may be different if you use an analogue pedal clutch.
Bob Smith once made graphs for all cars, I added pics of them below. But remember that all engines were altered in that clutch-heat patch after he made them, so I dunno how accurate they are today.