How many of you out there have successfully overwintered Trachycarpus Takil in Zone 7 with minimal protection? What do you think the absolute low this palm can take?
Your biggest obstacle is finding a true "takil". T. fortunei and T. takil are often hybridized and traits of either one emerge at random. A true female T.takil tree needs pollenation from a true takil male. With this intermingling, true takil is a difficult beast to leash.
If you do locate takil, I'd certainly give it a go in zone 7b anyway.
Plant Delights Nursery swears they sold me T.Takils, but I guess what I am really getting at is will T.Takil be that much hardier than T. Fortunei in Zone 7?
Reports are mostly what we have to go on with T. takil. Few people can really give first hand accounts, such as side by side comparisons of fortunei vs takil in zone 7.
Those that report say yes, takil is hardier although it's maginally so. Perhaps 5F or so, enough in a borderline situation. There are no assurances here since many factors contribute to success and failure.
Is there a palm society in your area that you can join and get info on, in your region?
I am in the process of joining the SE Palm and Exotic Plant society, but in the US, our "southeast" goes from Delaware to Florida with everything in between. This presents a problem for advice even within my home state of Virginia since the tidewater and Virginia Beach areas are Zone 8a and the mountains are Zone 5b in some places. I feel like I am in a no mans land in gardening in general since some warm weather plants like Camelias do fine while birch trees will bite the dust from the heat and humidity, plus a winter that is too short and too warm. Some folks have done well with sabals while not enough have grown Trachys, however, there is one success in Alexandria and the palm is now over 13 feet tall.
Sounds like a good opportunity for you to become a pioneer of sorts, with palms & exotics for Virginia. Perhaps in 10 or more years people will seek you out for advice on such matters.