I prefer the Hi-Spec 4-pot callipers because they give much better feel. I found the original Girlings to be a bit wooden. They stopped the car all right if you pushed hard enough on the pedal, but I didn't get much sense of what was going on at the tyre.
My experience with the Roadster was the same. I was going to upgrade, but changed the car.
The AP Racing 6 pot calipers on the Plus 8 are more than powerful enough, for anything! 8 laps of Castle Combe and they were totally unchanged. No fade, no nothing.
