I created a solo quick play for WRC2 that includes every single location, and in each rally I have all 12 stages in about half, and in the rest I have all 12 stages + 1 repeated stage.
I have done this in various AI levels from 85 to 95% and have experienced severe drops in ai performance.
The first few stages seem to be working at an expected AI performance depending on location, but after between 6-8 stages the AI drops dramatically to be at lease 1.30 minutes behind in short stages, long stages o have seen up to 5 minutes behind.