ok so the mini S (R52) i have on order will be in next week. I already know its going to need some more power. so when its broken in it will need a pulley

which one has the best result ? (i looking at 15%ish reduction )

i'm looking for somthing reliable and with a nice power increase.

Do i need a tune / ecu reflash / chip / what ever its called for minis.

thanks