General Rule of Thumb for Trachycarpus hardiness.
A lot of postings relate to the survivability of Trachycarpus fortunei and cold-hardy Sabals in colder Winter zones. I think a good rule of thumb is the long-term survivability of Magnolia grandiflora (Southern Magnolias). If your area has established trees of greater than 10 years, you should be able to be successful with the cold hardier palms with either no (or limited) Winter protection. These trees tend to be a good plant 'indicator' species of a solid Zone 7 (around the minimum for 'cold' hardy palms--assuming they are not going to be protected my thoroughly.
Took this photo this afternoon of one of the Edith Bogues (a NJ native)
Here is a link that might be useful: