Like I wrote, I have AI set at 100% and I have no idea how to make 'm go faster. Wherever I find optimised AI lines, I install them to check. In several cases AI behaves better (or worse) but very seldom faster. And in all cases it also depends on the used car.
I test all my cars on the same track, same conditions, stock setup to compare laptimes.
Even when I know I'm not the fastest driver, my lap times are consistent and after a few laps to get used to a new car, I will be lapping at a pace that stays within a few hundreds of a second.
I wish there was a way in AC to speed up AI like in rF2, where a slider lets you move them up to 130%. Impossible for me to keep up with them but at 100-120% (depending on car/track) I have a real race on my hand. Very difficult to qualify in pole and even then they are constantly on your tail. Very rewarding to get a win there