There is no general answer or rule to this because there are so many variables with the rider's size, proportions, weight, and the conditions and length of a race or ride, and even psychology comes into it. The only sure way to know for each person is with objective testing with stationary equipment or measuring on course performance. The answer will even change for each rider as their fitness becomes more or less, their age etc..
If someone dares to think they can be psychologically objective and test their current performance on a course or testing equipment with different length cranks, frames etc.. then they might get some answers, otherwise probably none that will make a performance difference. It is like someone believing their car will have more power because someone else told them if they bolt on this "hot rod" part that is what will happen, but a real tuner of racing engines will tell you absolutely that unless it is proven on a dyno or on the track the talk means nothing.