Considering that size fits great on a 17x7, I'm thinking that adding 1.25 inches of rim width is going to be less than optimal. Edit: Looks like Jason won the quick draw there. Everything I've read has said 7-8, with 8 really pushing it.
Lol, it really isn't that bad at all. I see more stretch everyday on factory cars such as M3s, M5s, M6s, etc. It's really no big deal.
8.5 was maximum stretch distance. 7 to 8.5 isn't the "optimal zone" or anything. It is just the range where the tire wont shred itself. 7" wide is the optimal width for that tire. 8.5 is more of the "yeah, it'll fit, and you'll be fine, but there are better options that actually perform the way the tire was intended to perform"
Stretching a tire isn't the same as having a low-offset/convex wheel (which is what BMW has been doing lately). Do you have any pics you can post up?
Here you go. This is a crappy cell pic from last summer on the way to lake of the woods. My car was filled to the roof with coolers and fishing equipment, hence the sag. It's all I have at the moment.