We use a spring type clutch as it is kinder to the driveline. We used to use the puck type in the SMs but I didn't really see any difference in times but certainly felt that the clutch was harder on the driveline. I have never used a puck type in an IT car.

I think there is more bang for the buck in getting the lightest pressure plate you can find. Spec and others make pressure plates with an aluminum ring surfaced with a replacable iron friction surface. These drop a lot of rotating weight, the old Z one I used to use was around four or five pounds lighter than a stock one.