I've played around with this a little over the years and have come to prefer a rod somewhere around 11ft long for this purpose. If you are not strip-retrieving the fly close to shore then a longer rod is probably fine although not really necessary. Also, if you are swinging the fly in current after overhead casting then a longer rod is great.
Extra length works against you on rocks, a boat, when wading especially, etc. If you are fishing for fish that hunt their prey too much rod reduces the fishability at the end of the retreive, the 'red zone' on the beach when most fish hit. Too short and you might as well have a single hander though.
The best choice will depend on the fishery and your approach to it. Even in the northeastern shore there is a place for full spey action rods and floating spey lines albeit practiced by a specific group of anglers who fancy the technique.
The CND Atlantis is designed for hunting the hunter on the beach and works well with shooting heads, full lines and shorter length spey lines. It comes in an 11/12wt and a 9/10wt model.
casting clip