Overall width, not so much length is the magic number.
Cat's, especially the larger diameter tube rigs, tend to get a whole lot wider than a raft of the same length.
For example - say you have 16x25" tubes and want, as you describe it, a day or overnight frame. The frame will need to be around 34-38" wide between the tubes, minimum. Add the diameter of the tubes to the inside width of the frame plus an inch or tube more as cat tubes tend to gain a bit in width when you add weight to em and you end up around 88-90" wide, easy.
The average 16 foot bailer will have 21-22" tubes, 40-44" between em and be around 84-88" at the waterline, loaded. The S/B can haul more gear, usually 20-30% more, by weight, and has more capacity, by volume than even a 90" wide cat.
A couple extra inches doesn't seem like much until it's what's between you and the line you need to take through a rock garden.
Cat's sure row nice when you've got the room, though...