In regards to the AI difficulty part, I just follow this difficulty calculator
I do as it says and go into Time Trial with the equal performance mode and just set several laps. I just keep lapping until I set a few consistent laps in a row within a couple tenths of each other and then plug that time into the calculator. Then from there I might tweak it a little bit based on practice. It definitely is a little time consuming but worth it. In the process I also just get a better understanding of the track and improve on it so that's nice. For nearly all my races I'm battling with the teams who are close to me in performance. I haven't really had an issue with the AI straight line speed yet either, but I've had to lower the downforce i'm comfortable with several points to keep up, and also I guess since I'm in season 1 and the 2nd to worse car on the grid or my difficulty is too low the AI speed thing isn't an issue yet. With the difficulty calculator I've had races with the AI at 85 all the way down to 70 for my worst track. Picking one difficulty would just have me all over the place and make it less enjoyable.
Just my two cents
Ai is currently in need off. Fixing and so are practice programs. Especially the qualifying program(completely broke) until they are fixed your better off just getting a feel for career modes than trying to setup any serious long term career. They are working on it. And hopefully the next patch will address those issues
Then also with the performance rankings you’ve got to consider what performance upgrades you have…. For instance you could max out all the brake upgrades and that could put you at number 1 in the rankings. Does that mean your car is going to be as fast?
upgrading your car and knowing what to upgrade is key…. Weight reduction, and drag reduction, ers. Give most bang for buck
