I had PR2's on for a while and really liked them, they always felt good and inspired confidence. Earlier this year I got PR4's and initially they felt good, however whilst over in Europe in mid July I had a few scary moments with the front end slipping out on long corners in the Black Forrest and that didn't fill me with confidence for the Stelvio and a few other high alpine passes. Fortunately few of the turns there are not that long so it wasn't too bad, but obviously it was in the back of my mind and undoubtedly affected how I rode - I still enjoyed it though.
I'm going to talk to the place that fitted them and see if they've had any similar problems or if it is maybe pressure related, I'll let you know what they say.