I have seen and heard the Porsche guys using the A6 Hoosiers, they have nothing but great things to say about them. If you plan on using these for autocrossing only as a second set of wheels, then I would use them. They do come in a decent lineup for use with the 15" wheels. The largest 15" they have I found was a 275-35-15, with plenty of choices for the front.
Jeff
Hoosier A6
Hoosier Size Chart
I found these FAQs after posting ....but I was reading up on Hoosiers heat cycling they offer and this link has a jag of infomation at the bottom of the page.
Heat Cycling FAQs
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