There's a lot of stuff your test doesn't take into account. Your tests are interesting but subject is really critical.
Retiming (Optical Flow) can often introduce all sorts of ugly artifacts ("swimming" etc) when shooting complex objects. Basically Optical Flow can make all sorts of mistakes. Try the same soccer ball in the middle of a soccer match while players are running around each other for example.
Extrapolating/creating frames is often not as good as having the actual frames. In simple tests like yours it may not make as much of a difference. IMHO have more temporal resolution at the source is generally better.
Basically Optical Flow is good for simple subjects with non moving background and the subject doesn't cross the path of other objects. I don't find that situation in my shoots.
Shutter speed impacts motion blur and its use may depend on the desired aesthetic. If one wants to simulate a hight speed camera than higher shutter speed is better.