While Vinny doesn't need to worry about winter tires in MS, I have found a benefit to 18 rims. Blizzak's are available in 255/70R18 and this is an application where the narrow width is actually beneficial. There is not really a good sizing for 17's.
In steady driving, I.e., highway cruising, the wear on tires front vs. back should reflect the weight distribution front to back. more wear on the front tires. For mostly city driving, under acceleration there would be more wear from the drive tires -> increased rear tire wear, but that would...