Ok so I turned the temps off and did some extensive testing yesterday and finding were pretty much exactly as I suspected.
Quick race at Melbourne, in McLaren as Piastri, so I'd know I'd have a fast teammate (pace stat 90+) to compare to. Weather clear, short quali, 25% race, no assists, recommended setup with onl minor front wing and brake bias changes.
On 103, qualifying without going mental or using blatant exploits like extreme track limits or anything else, I was a bit slower on 1st runs than Lando and on 2nd run I did what I called a damn good lap, but something I could probably do again without needed 10+ flashbacks lol. Ended up side by side on the grid with Lando just outside top 10. So to me that seemed pretty much exactly where the car should be based on performance index.
Restarted on 104, all the same and ended up 2 tenths off Lando, which given his speed, me still being new to game and Melbourne not being my BEST track I thought was fair.
I started the race on 103, OH MY GOD! I got past him and a couple others in the lap 1 mayhem but as soon as things settled Lando was lapping soooo much faster than me it was a joke. When he caught and then passed me easily with drs I was then able to hang on with drs and save battery, but as soon as I passed him he would be back through short time later when battery got low, so fair to say he had a SIGNIFICANT speed advantage and was just towing me along.
I went back and did everything again, qualified almost exactly the same, just 1 spot/1 to 2 tenths off Lando but started the race on 97.
Wouldn't you know it, he's a bit faster than me but now it's a case of he can pass me with drs when battery a bit low or I make a mistake and I can then pass him with DRS, so we're basically matching each other swapping places. I would say he probably still had a slight advantage due to consistency vs me being a bit slower and faster lap to lap but otherwise pretty close. 96 would have been less "sweaty" shall we say.
So that's about a 6 to 7 drop in difficulty setting in order to maintain similar relative performance from quali to race. I then used this same approach for first 3 races of my team, qualifying on 103/104 then racing on 96/97 and found each time I'd over qualify by a little bit ie sneaking into Q3 in a car that probably shouldn't be in Q3. Then having similar pace to cars who were a bit slower than me in quali who really should've been a bit head of me. But tbf being a not perfectly consistent controller user I'm better at getting 1 really good lap on fresh tyres than doing it over and over in a race 🙂
So for me anyway it would seem that track to track on this game that a difficulty drop of 6 to 8 between quali and race is required for a consistent AI experience between sessions.
Having also now watched the youtube career videos of the likes of tiametmarduk, aarav, jarno opmeer and more who all are making comments about the AI being "fast in the races" this seems pretty accurate.