To swallow the largest prey item, a croc monitor(largest oral opening). To digest the largest bolus, water monitor, largest stomach. And the best ability to get very hot without overheating(they can lower their body temps the most efficient).
JeffL had a nile that was given to him, that he gave to a zoo in Fla, that was about 6 1/2 feet, I got to hold that thing, I have no doubts that individual could swallow a med adult cat, but most likely not a large adult(but it may). I do question if that nile has the ability to actually kill a healthy cat. Most likely couldn't catch it, unless the cat was in a self destructive mood.
I have read the the largest nile was just shy of nine feet. I would think that individual could swallow a large cat.
Of course, this is a question of extremes, the largest prey item must relate to the largest individual, not the average of any species. Althought they may be one in the same. Thanks for the fun question. Cheers