Great lap time at Thunderbolt! I assume that is without the Chicane? Here are some thoughts that come to mind after reading your post, hopefully some of it is helpful.
- This is really tough to assess without digging deep into your data traces; however, break down Thunderbolt into 3 or 4 solid sectors, then identify what your best lap would be if you strung your best sectors together. How far off was your best lap?
- Be careful with making adjustments to your settings with R888R tires at 40HCs. They are going to be more than a few seconds slower than when new.
- There is a new AI data acquisition tool that mounts to your dash called APEX PRO. Basically, by using a series of LEDs, it attempts to answer your exact question in real-time. I've seen some pretty good reviews on it and you might want to look into it further:
https://apextrackcoach.com/
- You mentioned 'driving the school line'. You might want to check out some open track days with no-point-by passing. Driving off-line so frequently adds another challenge to train yourself on and helps teach you how to carry speed through corners in ways that normal DEs do not 'typically' allow.