I would have to agree that Chicago is the best option possibly not just in the area but in the whole country and maybe in the world for a fast time in the fall. There are a few things you have to consider: people to run with, organization, and minimizing uncontrollable risks. If the crowd helps you get through a race, that’s another thing to consider.
There is no question Chicago has people to run with. If you’re shooting for 3:00 or under, from what I hear, you have enough people to run with without having to worry about the masses slowing you down. No Wisconsin marathon has the numbers Chicago does. If you’re looking at 3:00 or under, there’s a real risk of running alone in any of the Wisconsin marathons. As for organization, Chicago has that covered, taking care of everything a competitive runner should need for a good performance (except the training and race execution) and more. Minimizing uncontrollable risks is a key one as I have found with my two Lakefront efforts. With Chicago being a loop course and spending a lot of time among tall buildings, the wind is less of a concern than it would be at something like Lakefront or Fox Cities and the scheduling of the event gives you the best chances of getting favorable weather conditions. As for crowds, nothing local can compare to Chicago.
This is not meant to be a knock on the Wisconsin marathons. They are very good at what they do. However, they simply do not have the resources to put together an event like Chicago. After my two learning experiences at Lakefront, I can not with a clear conscience tell someone to go to Lakefront or another small marathon with the same risky variables looking for a PR or other time goal. It’s too easy for variables that you have no control over to remove any chances of reaching such a goal.