You might try
Bob3 on this board for information about the northern end of Green Bay - he hangs his hat in that general vicinity for part of the year and might be a good resource. I think you'll find that there isn't a lot within a RIB ride, however. Your end of the bay has always been less trafficked, which means fewer calamaties. There have, however, been reports that a wreck has been found near Poverty Island which may turn out to be the
Griffin, lost in the late 1600's. That would be something special to dive...
Further south in Door County there are a number of wrecks definitely worthy of diving; too far for a RIB, though you could trailer. St. Ignace and the Straits of Mackinac have some great diving as does Paradise and Whitefish Bay. Neither are real close, but still doable as a day trip.
The Fitz is off limits these days. She sits in Canadian waters and the gov't there controls access. Then again, she's deep enough that only the very...brave...would even consider diving the site.
A good book for any Great Lakes diver to have in his bag is
The Great Lakes Diving Guide by Cris Kohl. Many dive shops in the area have it in stock.