I'm using Racing Brake 2 piece rotors with YellowStuff pads. The pads will rust the rotors after a rain or washing. But have no judder. The YellowStuffs are a bit dusty.

How many miles on your Z? Maybe the pistons are sticking? Z1 has a caliper rebuild kit for ~$50 (I think) for all four wheels. I'm wondering if that might help your situation.

Surely possible (70k miles) but for all four to begin sticking simultaneously seems a bit ridiculous. Even though the rears are much worse than the fronts, for both rear calipers to go at the same exact time seems a bit strange to me.

I was looking at the carbotech pads and they seem to have solid reviews; might try those soon. In the meantime I think I may start by replacing the brake fluid to see if that changes anything. About time it should be done anyway.

Ok, then. I've got 80K miles on mine and no issues whatsoever, so you may be right. And yes, very unlikely for all of them to go at once. Hrmm...