6th gear is very tall; shifting at 8,400 drops you too low in the power band (6,900 RPM). Short-shifting to 8,200 keeps you above 7,200 RPM post-shift.

Mastering the Assetto Corsa Porsche 911 GT3 Cup (2017): The Ultimate RPM and Shifting Guide

The KS_Porsche_911_GT3_Cup_2017_RPM mod has received widespread acclaim from the Assetto Corsa community, with many users praising its accuracy, detail, and performance. The mod has been downloaded thousands of times, and its user reviews are overwhelmingly positive.