Could you possibly give us a few fps shots while the field is lined up for the start, at Tetre and perhaps Indy?
Here's some results. System specs are in my profile. 2560x1440. All GFX settings on max, except:
AA - Level 4
Post FX - Medium
Shadows - High/Shadow Blur - Optimal
Rain Drops - High
Visible Vehicles - 12
In order to keep us vaguely on-topic, I hereby present my findings as screenshots

I'm driving a GTE Aston Martin, in all screenshots at least one Senna GTR is visible.
Qualifying Session:
Formation Lap, at Tertre Rouge
Formation Lap, at Indianapolis
Clearly, and not surprisingly, there is a massive difference between 12 visible vehicles in cockpit view, and all 40 visible from trackside cams.
I would've thought a minimum of 50fps in such circumstances is pretty good. The most important thing is, once the race was underway it was completely smooth.