The advantage of multi piston brakes is the ability to control pad taper. You tailor the clamping force with piston diameter.
Contrary to popular belief, Yes, a 6 piston caliper and larger rotor can be packaged to fit inside our common 15” wheels.
This is a Wilwood SL6R on a 12.75X1.25 Rotor inside a front Trigo.
So long as you keep the rotor near the spindle, there is no problem with clearance.
However I will say, for all but the extreme high speed open track cars, few need parts this big. Ultimately, you would want the smallest, lightest system the can repeatedly stop the car from its highest speed, without fade. Obviously, a 300 hp street car that sees a little open track time, has a much smaller requirement than 3170.
Imo a 4 piston caliper and 12”x.810 rotor would be more than enough to deliver all the braking performance you could want with less weight and at a lower cost. Just get your pedal ratio and M/C bore size correct and you’ll be happy.
IMO, for the money, there are better brake packages than the the SSBC deal.
JASON