Here is a good illustration of the size difference between a 6-piston Brembo caliper, found on a Hellcat and Scat Pack Widebody, and a 4-piston caliper.
I've had the opportunity to own Challengers with all 3 types of factory brakes offered, 2012 5.7 R/T (275's), 2015 Scatpack (275's), 2020 Scatpack widebody (305's). I can attest that there's a big difference between the single piston base brakes and the 4 piston brakes, like night & day just in initial pedal feel and shorter stopping distance. The difference between the 4 piston & 6 piston is still considerable, but less in the initial pedal feel and more in the stopping distance. Part of that could be in the wider 305 tires & suspension. Just my experience.
As far as maintenance goes when having to replace brake pads and any other brake maintenance is there a big difference in cost of maintenance between the 4 piston and 6 piston brakes?
Yes. 6-piston brake kits are more expensive than 4-piston ones. For example, Jegs sells a 6-piston kit for the Challenger front, consisting of Powerstop Z26 Extreme Performance Street pads and slotted/cross-drilled rotors, for $508. A similar 4-piston kit costs $355.
Don't really see the need for 6 piston calipers unless your planing on doing a lot of course racing. Otherwise the 4 piston will, in a panic stop, try to make your teeth pop out of your mouth.
Same here. I am very pleased with the performance of the 4-piston Brembo set-up on my 2009 SRT. Road & Track magazine stated that my Challenger will stop from 60 mph in only 121 feet and from 80 mph in 212 feet. This is great for a 4,200 lb. car.