I think you're joking but...
Felt made a rigid drop bar race bike designed around the 60mm or 70mm Schwalbe Big One tires. I think it was purposed designed for the beach racing they do in Europe. Guy and his wife had were each on one at an event I did in Alabama. It was a neat bike and the tires seemed to help him on the rough descents but he really suffered once we got the paceline up around 20-25 miles an hour and the short punchy hills seemed to just sap his energy. He dropped before the finish so I wasn't able to get a picture of his bike but if anyone knows the model please let me know I'm interested to see what it was/is. I didn't see anything on the Felt website.
Anyway, I think the point of diminishing returns is around 45-50mm width; any wider and the tires start slowing you down more than speeding you up on anything considered a gravel road.