I was considering getting 10mm spacers for the rears but these actually stand out just right I think. Pretty much in line with the top of the wheel arch.
go michelin Pilot sport, far better tyre. I have Potenzas on a 35i that I bought about a month ago, they are not a patch on my pilot sports fitted to my previous Z4.
The dead giveaway is that they squeal on smooth concrete i.e. multi storey car park, squeals mean crap rubber because its slipping, pilot sports are silent as the grave have the best wet stop rating and wear rates are exceptional.