I personnally don't like to use spacers on a 911, but again that is just my personal preference.
If you can swing it financially, I would go with 9x16's in the rear. Here is a pic of 9x16 on the rear of my '84. I am using 245/45-16 tires. This combo fits fine with no rolling of fender required. If you mount your 255's on the 9" Fuchs, you may need to roll the rear fender, but I have no experience with 255's.
