Porterfield R4S pads are great agressive street and moderate track pads. The R4 or R4E are the full race and endurance race pads. I have used all three compounds both on the track and street. The R4 and the R4E are acceptable on the street if you don't mind the noise and dust.
The R4S pads work well on the track at 8/10th or less. Pushed to 10/10th they just don't hold very well. I went through 75% of a brand new set of R4S pads at a single track day when we double stinted a heavy car (BMW 535i) and DID NOT bed the pads properly BEFORE the track event. Of course that was also letting a Porsche 911 driver track my BMW. An Agressive 911 driver is used to braking very late and very hard.
I'm currently using Porterfield R4 pads with 911 SC brakes on my 914/6 2.7 and they work pretty well. They will still cook the fluid without sufficient cooling.
Eddie