I don't know about a LOT of extra room. I have a 30 qt. pot that came with my propane cooker (pot is a real POS, but it works) and there isn't much room after I collect my sparge water. You just have to be careful when you see the hot break coming, really cut back the heat and stir until it passes.
I have a 36.5 qt pot & fill it about 1.5-2 inches below the rim. It is a bit tight, but I just tend it like a mother hen when it starts to boil. Occasionally some will burp over the top, but I put up with this because I want to maximize my 7 gallon fermentor & carboy. Also, I usally have a mop handy #:^),