I did a test last year with the GT3 (granted it is different car/engine): On one of the tracks that I visit often (Summit Point), on the front straight, we shift from 3rd to 4th and to 5th before braking for turn 1. I used to short shift from 4th to 5th right around 8K RPM normally. On multiple sessions and different days (low and high temps), I ran it to 8500 RPM before shifting to 5th. My data logger recorded, in each of the cases, 6 to 8 mph higher speed before braking and 0.2 to 0.3 lower times for the straight
My point is that sometime we assume there isn't much to be had with an NA engine up top, but this was a surprising finding for me.