My system was a major difference over stock even with the drums it produces respectable stopping performance. Especially noticeable at 80-100 mph when you need to scrub 30-40 mph quick. FWIW - I did the upgrade this year.
I initially wanted 6 piston but couldn't justify the $$ for the application. The C5 calipers appear to offer more bite than tires can hold at lower speeds. If I had a track car I'd probably go 6 piston for fluid and cooling capacity. Don't know if I'd go 14" rotors over the 13" due to un-sprung weight. My 13's weigh 29 lbs. each.
