Guys, I used to do 15 BBL boils in a 500 gallon brew kettle. Yes, I had the rare boilovers, and it was my job to clean those up.
Granted, homebrew is done at a much smaller scale, but if you monitor the boil, you can do a 5 gallon boil, in a 6 gallon pot. (But, it is MUCH easier in a larger pot!) (We also had a product called "No Foam," that would completely wipe out any foaming up of the boil. It would break down, and not hurt the head on your beer. Took a tablespoon, in a 500 gallon pot.)