Don't want to hijack, but curious. The PO on my -6 had some nice big and red Brembo GT front calipers installed, along with:
Install front struts / housings
Install tie rod ends
Install ball joints
Rebuild rear calipers (former front)
Fit & Install rear brakes"
Car now rides on 16" Fuchs, the original 15s wouldn't clear the calipers up front. And the original rear calipers disappeared - I'm left to assume their sale was a nice $$$ bonus for the shop that did the job...
But I've been keeping an eye out for 16" space savers as a result, and am curious to hear that you need a 17. I'm assuming you've tried 16's and they don't clear. It just leaves me wondering about what-all I've got under mine, and whether a 16" spare would have an issue.