ACS 8 pot calipers

They are actually just rebadged Brembos-albeit they look great. You also have to be careful with the 8 piston setup on the M5 as many times its master cylinder doesn't provide the push needed for a firm pedal feel. Many times the bmw m5 tuning is best off with a 6 or 4 pot caliper setup. I am sure Dave Z can provide more answers on that.

I agree w/ TCM about piston's. If you choose to upgrade your brakes I would state IMO go w/ Brembo's. They worked it out where it is a perfect application. You do not need to worry about master cylinder size. All has been worked out. I called Brembo and spoke w/ them before I did my upgrade. The piston sizes in the calipers are exact design for our cars.

I went monster w/ the front 16" rotors and rears 15". Running the front & rear 6 and 4 piston calipers. I love them and they look stout.

I had HRE make me a pair of rear C20's in 18x11" that will clear the rear rotor. This way can run a drag radial for the strip.

I've seen the set up by RDSport which looks very good but they do not offer a 16" (405mm) rotor.