I searched and found some comparison of brake piston sizes:
E92 M3 Front: 60mm
E92 335i Front: 57mm
E82 135i Front: 28mm+32mm+36mm (equivalent to 55.71mm single piston)
E92 M3 Rear: 46mm
E92 335i Rear: 44mm
E82 135i Rear 42mm
References:
https://www.e90post.com/forums/showp...5&postcount=34
https://www.racingbrake.com/Piston-K...W-p/bb-61p.htm
https://www.racingbrake.com/Stainles...r-p/bb-21p.htm