Having not run Fox Cities, I can only give you my experience with Lakefront.
In 2003, with absolutely perfect conditions, I ran 3:07 for my debut.
In 2005, with it being a bit on the warm side (close to 70 at the finish, last 3 miles with a 10 mph headwind), I ran 2:59.
Unless you have severe headwinds out of the south, Lakefront is the best course for a BQ assault of the 3 fall races in Wisconsin, in my somewhat biased opinion. You run the majority of the race in the shade (east side of street when heading south for 17 of 1st 23 miles), it is flatter than a pancake, and there will be plently of people to run with btwn 3:05 and 3:15 pace - more so than Fox Cities. Maybe you don't need that, but I think it's good to have people around you. You already know the pros and cons of Whistlestop.
Of course, you are closer to Appleton, and there is an advantage to sleeping in your own bed the night before a marathon vs. being in a hotel.
It comes down to what are you most comfortable with. I've never regretted running Lakefront. Even though I passed up a chance to run Chicago on my 40th birthday for my 1st marathon, I'm convinced I ran the fastest possible time on that course.
Heck, if you run Lakefront, I'll even help devise a pace strategy for you, based on what pski planned for me last year. It worked to perfection, but it made some curious looks for the people running along side me when at mile 7, I said I was going to slow it down for the next 10 miles.
Now, I hope you and Adimal are running comfortable 35-45 mile weeks about now, ready to kick it up to the 45-55 range come 5 weeks from now