Stay staggered or is square an option?
 

I have the typical staggered 18" Turbo twist rim set-up on my 2000 S.
I found a beautiful set of 18" Carrera rims like those on the '04 550 special edition model, but alas, all are 18x8, there are no 10" wide rears that this person is selling.
Would I be best advised to stay staggered, as this ostensibly reduces oversteer and increases rear grip? As of now, this is a purely street-driven car. I have not yet been to a track of any kind, and can't see it happening anytime soon.

With 8" wide rims you could run square 225/40/18. It would work fine on a street car.

I have considered running 8" all around since I can't find any 9" but I would not put 225/40/18 on the rear. I am a prospect for that set of 8" if you pass Boxster Steve.

There are a few posts about running a square set up in the Racing section. Do a search on "square setup".