cats follow the food. sure they spend a lot of time on or near bottom, but i ran into a situation last winter when i was catching bluegill suspended 10' down over 20 fow. suddenly the bluegill bite cut short and i caught a dozen 1 lb. channel cats. even in winter, they'll swim way away from bottom looking for food.
i have yet to be successful with a float rig for cats, but that's simply for my lack of knowledge and practice. most likely, i'm using the tactic in the wrong location. i know where to find them if they're sitting on bottom, waiting to ambush prey from piles of brush and such, but i don't know where to look when they're suspended.