I thought this was a pretty good testament to the difference in hardiness between sabal palmetto and birmingham sabals. I don't think we got below 10F to 12F at my house this winter, though we did have a spell or two where we went between 2 to 3 days without getting above freezing. We had a few small snow events, none more than about 1.5" at a time. The birmingham is in the SW corner of an L-shaped bed on the south and west sides of my garage. Both are shielded from north winds by the house.
Here is the difference between the two at my house given the above winter conditions:

Birmingham



And about 5 feet away, in a more protected spot, here is the palmetto.



Still alive and pushing a new spear.



That palmetto is sheltered by the garage on the east, the house on the north, and is almost completely covered overhead. The birmingham performed pretty admirably, I'd say.

As a side note this birmingham was sprouted from the very last seed batch from John's notorious Tulsa birmingham. Of the seed he gave me (several years after his died), it was the only one I got to sprout.