You're right, it's definitely a '
Koelreuteria paniculata Laxm.'
I've got one in my garden, so it's hardy to at least zone 8.
Very nice autumn colours. I usally trim back the year's shoots in July (more than 1 metre long!) and it backbuds profusely.
I'm planning to pot one of the many seedlings around, but like
Rhus typhina, not much of a chance to get something decent with this tree: the leaves are too large, and cuttings are difficult to heal.
Goes well in a pot though, the one in my garden comes from a seedling I left in a pot for several years before finding the right place to plant it.
More info
here