Blue-crown would prolly do alright... Or anything that you can cut back & keep inside for the winter.

Sunburst supposedly can survive that low, and edulis might be a contender but I haven't had the oppertunity to test either's hardiness.

If they get big enough in the summer you might be able to mulch the roots well enough that it will regrow in the spring.

Or just have all your pots on rollers. When it gets cold unwrap them from their outdoor roost (being sure to try & root & trade whatever you have to cut off) roll them inside to that bright sunny window or hang a 30 watt circline bulb above them & let them grow slowly for the winter. Then when it warms enough in the spring.. Outside they go again.
Sounds tedious, but it's what I did when I lived in upstate NY. My apartment was an absolute jungle in the winter(s) with vines growing across the celing...

Iam in a colder part of zone 8. I have both the blue crown and Constance Elliot that are in the ground and are evergreen. They are in full bloom now after a slight freeze a couple of weeks ago and a frost last Saturday. They have survived down in the lower teens but have been burned at that temperature. I also have incarnata and incense in the ground. They freeze back at first frost and then come back as soon as the ground starts to warm in the spring. I can not mulch anything as my chickens and guineas love to remove it looking for bugs. All of these have been extremely hardy for me even without any protection.

Patsy