Enjoyable experience is a very subjective thing. For me it's about keeping the framerate above my refresh rate (since I'm using vsync) while still having a decent amount of eye candy. For smooth and stutter-free gameplay.
I guess you'll just have to figure it out for yourself: What's the minimum framerate you can accept with how many cars on the track, and at which graphical detail.
Once you figure that out it's just a matter of driving some laps, watching the replay and keep an eye on the fps and adjust settings accordingly. Then repeat the process until you are happy. That's is what I did, but of course others might have a completely different approach.
The fps score is irrelevant at the moment, until we know how it's calculated, so I wouldn't worry to much about it.
They certainly can't be having something like that when the game makes it to console.
for never lowering that sooner, but I was always above "MY" minimum fps before getting to that setting. 
