When I was doing test races -- starting in pole against one other car in Custom Races -- I felt like the Opt time was lower than it should be. Not to the degree that you saw, but somewhere around 2-3 seconds. Maybe there's a bug with the way the opt time is calculated on that track.2
As for other race preparations, I've reached the point where my pace has plateaued and I'm alternating between feeling "This might be okay", and "I'm doomed".
I managed to get my fastest Free Practice lap down to 3:40.9 this morning, which felt like it was pretty close to as fast as I can drive that track. Maybe there are a few more tenths in there, but I don't see it improving much before Wednesday. It ranked in the high 2300s globally, so nothing to brag about.
I've been doing some full-field custom races for practice. I'd started by choosing Gr.2 opponents, but now I've switched to using the one-make setting so that I'm racing only against GT-Ones. That feels more realistic.
I'm starting to come to terms with heavy damage. Those AI drivers brake in the strangest places, which means I have now gotten a fair bit of practice driving with front aero damage after the inevitable contact. I'm learning to leave lots of room on the twisty bits and wait to pass on the long straights. I doubt it will be a useful lesson for the race, though, as I expect I'll be one holding other drivers up and braking at points that they find strange.
I tried a lobby race last night, with a mix of drivers. I was not driving well. I had a track limit penalty on all but 3 laps. It was in the dark, so I'm blaming that. I still managed to finish 2nd... after 4 of the 7 drivers quit.
Maybe this is okay. Maybe I'm doomed. We'll see.