I've been to Green Bay- actually used to live in De Pere in high school (east side). With as many concrete roads that the Green Bay area uses, I would definitely stick with a 17" wheel in order to have more tire sidewall and give better cushion. Both from a ride comfort and from a wheel protection stand point.
Not to mention, even the larger MSP brakes still look small behind an 18" wheel.
And my winter set up (15" wheels with ES factory sized tires) is significantly faster than my summer set up (17" wheels with the MSP factory sized tires). Part of it has to do with rotational inertia, and part of it has to do with the reduced gearing of the winter set up.