I ran HPS with the stock rotors during winter and they left deposits. I'm sure the shimmy you are experiencing is from the deposits. If you want better rain performance, slotted rotors can help a lot with that. I did a track day in pouring rain and with slotted rotors and track pads, I had no problems stopping even after long straights.
I cleaned up the car today and snapped some photos. I had to fix a small leak on the brake line fitting that meets the caliper. At first, I wanted to be careful not to torque them too much since they are brass threaded into billet aluminum. All good now though