Addiction,
My autocross buddy just put 245/275 setup on his 17" x 8.5" stock wheels.
( I believe he went with Kumho Ecsta V710's )
He is not running spacers and they seem to fit fine :
http://986forum.com/forums/showthread.php?t=15609&page=1&pp=20
( see Sammy's posts )
Hope this helps...
Nick