clownphish,
I just read your post about your conversation with the guy from dragonwheels.com. With reference to his comment about the spacers, he obviously doesn't know what he is talking about. I don't think you should rely on his advice. I know that with 17 x 7.5" wheels, + 45 mm or greater offset is advised to prevent tire/fender contact. With a 17 x 7" wheel you might or might not have a problem with a + 42 mm offset. Rishie points out that a P5 needs more + offset than the sedan to avoid clearance problems.
Tire contact can run from minor rubbing, depending on load, to ripping up the tire tread depending on severity. I'm sorry I can't give you a more definitive answer since I personally run 16" wheels on my sedan.
02 Dx Millenium Red