I ran heatsink yellows. They give incrediable bite and noise for me. They just had no hold, at all. That was on a grind on the rear, so i swapped them over, stuck them on a fully smooth rim with tar, but that was on the front. On the front they were awesome.
I wasn't overall impressed with there performence on a grind, saying that, Any brake ive ever used with a grind has been utter shocking.
Smooth ***.