I would make good use the posts and do the wider aisle. You won't regret that. You might make some of the stall dividers removable so you could open up a stall to be 23' x 10.5 in case you need the extra room, foaling stall or for a hospital stall situation. My stalls are about 11.5x16' as I wanted them large enough for movement if I stall for long. I rarely stall anybody other than my old blind appy and I wanted him to have space to move about. I'd think 10.5x11.5 would be roomy enough in most cases if they have adequate turnout.