Similar story for me. Used metalmasters for years , no apparent problem. I get about 40- 50,000 miles from rotors between replacement due to warpage. Is this from the pads? I don't know, but the rotors wear faster than the pads. OK, rotors are cheap. Fine for street performance and pedal feel seems fine. I got ATE pads recently from Blunt and I can't stop the squeal. I've had them out twice and re applied anti-squeal but it keeps coming back. Also, having to use wheel cleaner now to get the dust off every wash. Never had an issue with this before.
Is there test data to say the Porterfields give better performance? Or is this subjective?