At the lake we have a 21' Cobalt bowrider, big and heavy enough to handle weekends on Winni. At the boatclub I belong to we have a large percentage of pontoon boats and I have had the pleasure of being on a few. I would not take a pontoon onto Winni on weekends.
As a matter of fact I have a relative who is confined to a wheelchair, and while a pontoon would be perfect for getting him on the water, there is no way I would consider it safe. (severly handicapped) I had considered a deck boat which I consider a hybrid between the room of a pontoon and the durability and stability of a bowrider, but I haven't found one with the room in the bow to handle a wheelchair.
A Holiday Mansion would be too big!