Something in the back of my brain if fighting to get out regarding this...
I recall at one point, that was widely true for transmissions, and the result was a true 1:1 ratio, which is why 4th was perfect for dynos. It's been a very long time since that was true as a "go to rule" though. Even in cars, a 4th gear typically is nowhere near 1:1 anymore with gear counts escalating into the 8+ range.
On the rocket 5th is closer to 1:1 (its actually 0.96), where as 4th is 1.16:1. Theoretically we should all be dynoing in 5th not 4th, but people will whine and say "your numbers are high because its a 5th gear run".