i ended up going with a kokatat, fully dry. a nice feature on this suit is the zipper; while in the front , it is flat, so its not too uncomfortable. neck gasket seemed too tight when first put it on, but didnt even notice it when i was riding.
i wore it foiling. unreal comfort and warmth. especially when de-rigging. wow.
wore it boosting. it was ok, but i found it hard to regulate temperature. the amount of insulation you need to safely do a rescue swim in, vs what you need when boosting is quite different. wetsuits definantely regulate temp better. its still totally doable in drysuit, but i had to cool off by floating around.
the thing i worry a bit about winter foiling in drysuit is suit failure. if suit ripped for any reason, and i was in the water, pretty sure i would be dead before i could get to shore. i suppose it would have to be a combo of suit failure + not on board for while. probably wont foil too far from shore. .