I too keep all mediums. The usual winter configuration for me is three medium 8 frame boxes, with one of those being all honey. I see no problem going into winter four boxes tall as long as the hive is strong. Sounds like your hives are strong with three boxes of brood.
My concern would be that when that brood hatches they will go through the stores quickly, and there is not much out there to forage. Frankly one box of not yet capped honey at this time of year is light. My thought would be to feed, if you are not doing so already. With the weather still relatively warm the hives should be able to put some weight on in the next few weeks.