That depends....how long have you had your M3? I say go for the M6. But the Supercharger systems make the car whole different animal. but then youll want to spend money on new brakes and etc.
When it comes to mods** to the engine and brakes i prefer them from the manufacturer.
Currently:2016 GT3 RS LO/UV, 2015 991 GT3 Carrera White, 2016 991 GT3 Lava Orange
'16 /// M3- SOLD
'15 /// M4 -Sold
'11 E92 ///M3 ZCP - Space Gray - Sold
'11 E92 ///M3 ZCP AW- Sold