Are your rotors glazed? That's a common cause of loss of high speed braking ability.
I have PF Z-rated pads and notice they take noticably more pedal pressure to brake from high speeds, but they don't fade like most pads do.
If you are light to moderate on the pedal they don't bite very well. Hard on the pedal and they heat up and bite quite well.
I haven't been extremely impressed with them myself (I was expecting more from past performance pad experiences), but they are light years better then the stock pads were.
They do create a lot of dust too...