OK, thanks for the explanation Dan. I wouldn't think that there would be much PERFORMANCE difference in the snow between an 8" and a 8.5" width wheel when comparing the same size tire. Also, with an 8.5 tire, you can still use a 225 width tire if you still desired, right?
On the other hand, in the dry, the wider wheel width would give you the option to change to a wider tire (like 245 or 255) for summer performance and/or motorsports.
Weight is another performance concern, however, the added wieght of the 8.5" vs. 8" wheel is probably negligible when compared with the benefit of the larger contact patch and added grip.
So, I think that, a 8.5 width gives yout the most flexibilty in both seasonal extremes, allowing one to go narrow in the winter and as wide as you want for the summer.