I have to say, unless they are being prepared for someone else's specific wishes, I do a fairly high cut on my reds to remove the length of the nasal bones which means they fit into a 10lt stew pot, it is far better that way as I can get the heat there to really boil the meat off, I never achieve a hot enough boil in the bigger pot, but recently invested in a larger output gas ring which seemed to do the trick.
As CSL said, its the length of the pot diagonally that matters, as much as diameter, it doesn't have to be the deepest container, but I do find that the galvanised tub I use, being elliptical achieves this well.