If you track regularly you probably knew about the benefit of 6 piston vs. Depends on a lot of stuff.
Front 6 Piston And Rear 4 Piston Brembo Zr1 Calipers
6 piston calipers vs 4 piston. The calipers themselves are made from a variety of materials steel and aluminum being the most popular steel for durability and aluminum for weight. Thats because the pads are what 35 to 4 long. Depends on who makes it how it works with the car etc. Compare that to one of those really long 6 pads found in a huge 15 rotor set up. They are almost always fixed position calipers without a bracket similar to the 4 piston design. 4 piston so i would think you are not track junkie so i would say stick with 4 piston which will give you more than enough stopping power.
On 6 piston calipers you will usually be able to see the outlines of the 3 pistons on the outboard side of the caliper. 4 pot calipers means that the brake calipers are holding 4 pistons. The stock m3 caliper single piston is probably nearly as good as many 4 piston aftermarket calipers. The 4 piston calipers are going to do a very similar job at distributing x amount of force as the 6 piston design. Some say they arent happy with 4 piston stopping power and they shouldve gone with 6 piston. To answer your question i wouldnt pay a premium for a 6 pot caliper over any other caliper unless performance was dramatically better.
Different types of calipers the thing that holds the pistons themselves will hold different amounts and types of pistons. They actually have a lower profile than the dynalites so they will fit inside a 15 wheel with more clearance. A 12 brake kit with the 6 piston calipers cost about 300 more than a 4 piston kit. 6 piston calipers usually feature 3 inboard and 3 outboard opposing pistons. It fits the same bracket as the regular dynalite 4 piston caliper.