6th for max rev just before highest speed, in this case almost, as I had to compromise for long 3rd/4th see below. Meaning the "final gear" one tick lower and my 3rd /4th gear became just to short for my liking (having to shift just before 1st corner for example)
2nd gear (aka lowest gear) set-up to be able to accelerate out of slow(est) corner on a track, sometimes you use 1st (longer), but no need for that on Bathurst.
Other gears, see if you have to switch gears just before a corner, one click longer could help. Are there corners, you feel are really important for a good laptime, see if you can set-up your gearing for that.
So for Bathurst:
3rd gear for second corner, quick uphill right. Was in between 3/4, I choose long 3rd gear.
4 th gear for that quick part on the top of the hill (left handers), do not want to shift there, you want all your focus on the track, a long 4th gear helped with that.
Perfectly I would love my 3rd/4th one click longer, but with the available options, this was the best I could find (otherwise I needed to up the "final gear" setting and that slowed the car down to much.