What size tire did you use? I am going for the 8mm spacer but I wanted to go with a 225/45/rf17. My suspension is stock.

 

My suggestions is to NOT go with 225/45-17 tires. That size is too big and heavy for the Mini, in my opinion.

Go 205/45-17 if you want light weight and responsive.
Go 215/45-17 if you want a little bit extra grip, without a big compromise for weight and responsiveness.

I have 215/45-17 snow tires on my my OEM Clubman rims with 8mm spacers. I am lowered with ~2° camber all around, and the tires are just inside the fenders. Fit is really good.

 

+1 ^ Most do the 205 or 215 unless they track and need wide and sticky.