I've had some fun races in the DLC Capri using the standard setup against the AI using same class or identical cars racing at old Dijon and Silverstone International.
For some reason the AI lap quite fast in that car and provide a decent challenge.
Another fun was the Speedhunters Dodge Challanger against identical cars at Silverstone International.
Hoping to find some more good combinations next time I play.
I also tried the Speedhunters AMG SLS car against same class opposition at Silvertstone International, the PI on this car is only 1500, but it's very fast for it's rating and upto 10 seconds a lap faster than the AI. I was in the 1.15s and the 2nd place AI car a Lambo Murc 1.25s
With identical cars the AI are much faster and can lap nearer my times, which shows the PI is far too low, it laps as fast as cars with a 1900 rating.