I hunt over my hounds, using a 410 or 28 ga.sxs. If, and when I shoot a rabbit, I use #5 early season, and 6`s or 7.5 late season. (less cover to shoot through) I have noticed that the larger shot drives the hair further into the meat, but a sharp little knife will solve the problem. Larger shot is easier to find in the meat also. Nothing like chomping down on a piece of shot.
