I just had the 964 RS clutch installed, and I have had zero issues with idling. Well, ok, it's a little noisy with the clutch out, but none of the issues others have reported, such as lumpy idle. I had an Upsolute tune that was supposed to be reflashed back to stock before the upgrade. I sent the ECU program to Kevin at UMW, who is going to do the tune, and he said that the program is "mostly stock" whatever that means.

+1 on the GT2 clutch actuator. I also had the 997 SSK put in at the same time, and it's all really smooth now.

Jon