Last night, I tried something out on GP3 at EuroSpeedway.
I did a full 100% distance race. I changed all the car setups and in particular, the gear ratios. I had first gear at 75:64, second at 76:64, third at 77 and so on.
Anyway, I started the race and although it was a bit slow getting off the line, I reached 410km/h in 1st gear!!
I also checked the PO and it was only 10%. The lowest I have ever seen it.