I've got 4 piston Wilwood calipers in the front. The calipers are aluminum and very light.
The rear uses the same Varga caliper with ebrake as everyone else. In my opinion the rears are way too heavy, and I'd like to find a lighter caliper solution.
I changed the front pads to a Wilwood compound that works for street and track, with a wider heat range. Pretty sure it's Polymatrix Q which has has some ceramic in it.
I don't know the weight of each corner. The spindles are the same and the caliper brackets should be very close in weight. I know the CSP have very light hubs, and next lightest would be CB, then Airkewld. The SoCal ones have to be 10 pounds more each at least. I would assume the rotors are all around the same weight, it's the calipers and hubs that can pay dividends in weight-saving.