Thanks for the note on the yuzu vs changsha. It sounds like yuzu and changsha are close in hardiness.
Yuzu is more hardy than Changsha. These are not my only Yuzu and Changsha plants. I can see it in the color of the leaves, the exposure to cold does not cause the Yuzu leaves to turn as yellowish in hue as the Changsha, which I have found is usually is a good indicator of hardiness. (Although strangely the leaves of both of my two Ichang papeda plants turn very pale and yellowish, so maybe this is not always the case)
It seems like Yuzu is not all that much more hardy than Changsha though, although I cannot say for sure based on personal experiences.
This is purely anecdotal and could be wrong but I get the feeling that Yuzu can start growing vigorously at a little bit of a lower temperature level than Changsha, although both are vigorous growing varieties. Changsha loves hot temperatures though and might take off faster than Yuzu in climates with hotter temperatures.
They both seem to recover from damage well, which may not be the case with all cold hardy varieties.
I've tasted the fruits from both, freshly picked from the tree, and while the peels of Yuzu are tender and kind of edible, the peels of Changsha are definitely not. Most people will tell you the inside of a Changsha is better eating quality than the inside of a Yuzu though. Might only be a little bit better, it is a little subjective.
Its good to know yuzu is growing outside in Seattle.
I don't know how well Yuzu would grow in Seattle. Where I am has very slightly colder average winter temperatures than Seattle, but also gets a little hotter in the summer. The plants really need that heat, due to the cool climate and shorter growing season here.
As you go only a little bit north of Seattle, there are many areas that get very little heat most of the year.
That can be difficult to imagine for people who live in the South. There are some big climate differences despite the fact that we both may live in zone 8a.