There is no 'one size fits all' setting. If you are alien fast (which I believe you stated in another thread) then set the strength to 100% and see if they can keep up. They are generally slow in the low powered, momentum type cars.
Experiment with the aggression slider, at 0% they will still overtake, though they will generally be cautious and patient about it. At 100% they will likely run a slower pace because they are never content to sit and ride; if they are anywhere close to another car they will attempt to pass it right then, right there, doesn't matter if it isn't a safe place to do so on the track.
I personally like them at 85% aggression, for the most part. If I am simply recreating a track day I will set the aggression much lower, around 20%, that way they generally wait until a straight to pass.