Dom's tune and online testing is what made me go faster last night. Except I used -25 in the rear instead of -35, and did the tranny trick. No chassis reinforcement for me, but I do have 2 copies of the car, so might try it. Can also gift if anyone needs it. Using full downforce.
Turn 5 is the >90deg left before the uphill? Yes, that one's a bit hard, but it actually seemed worse in previous GT games, to me. I brake earlier than the driving line tells me and get back on power ASAP. I know, that's the recipe for almost every turn.
I finally figured out how to take the fast left before the cork without brakes or downshifting though: turn in way before you think you should.