Im looking at abbk and found this.
Wilwood FSL4 is product #120-7476-R/L with a piston size of 1.75" = 4.811 sq. inches
Stage II: Wilwood narrow mount SL6 is # 120-7228-FS 120-7229-FS with a piston size of 1.62/1.12/1.12" = 4.032 sq. inches
If the 4 piston has more sq. inches dousnt that make it better than the six? Or am I retarded and overlooking the obvious.
This is from on a dime performance brakes. Thanks

 

the primary advantage to increased # of pistons is better pad wear

as far as piston sizes, you have to then compare it to OE and see how they match up, to know if it will be a suitable match for the stock master cylinder