You probably have the hardiest palm there with R. hysterix. Be forewarned, they are not the fastest growers in the world. Sabal minor is quite hardy but most are EXTREMELY slow growing. Sabal louisiana is moderate in growth rate (for a Sabal) and relatively hardy (maybe down to 7a or 6b (with microclimate). You're pushing it though in 6a without winter protection. I guess I would suggest a position not too far from the house. A loose soil might help with excessive winter wettness. Of course, you can do a lot more (within reason) if you protect. I don't really bother and just make due with my Trachycarpus fortunei. This winter has taken a toll on it though. The leaves look horrid but the spears are nice and green. Trachycarpus is nice because they grow relatively fast and can even recuperate from spear pull. If you want to venture into this genus, try T. wagnerianus (protected some)--it's hardier than T.fortunei. Good luck!