I have the RS19 and they are incredible on track, even at Summit Main which is very hard on the brakes in the summer. Also hard wearing (5-6 events on them already with plenty left), and easy on the rotors.
But - I would not drive them on the street more than I have to, they squeal like an old school bus. People stop and stare.
2004 Z4 3.0
2014 X1 28i ED
2015 F80 ED in June