I always stay with the same brand for street and track pads, it helps to prevent this judder issue which can be caused by different pad compounds not transfering at the same rate. There can be a tendancey for deposits to build up un evenly and cause that vibration if different materials are not compatable. That being said, my track pads will always take 2-3 laps for them to get smooth by coming up to temperature, both pads and rotors. The hotter they get, the better they work! I like the Carbotech XP-8 for the track and Panther + for the road, FYI.