Here's my take...
supercar = exceptionally high performance
exotic = exceptionally low representation
exotic supercar = exceptionally high performance with exceptionally low representation
Z06 = supercar but not exotic
exige = exotic but not supercar
LP640 = exotic supercar
What the cutoff points are, ends up being a personal issue.
How high must the performance be to qualify as a supercar? (faster than 99% of other cars? 99.9%? 99.99%? 99.999%? etc)
How few should there be to qualify as an exotic? (1% of all cars? 0.1%? 0.01%? 0.001%? etc)