Hi James,
the decision what citrus is suitable to you location depens also on the conditions of the small climate of the planting spot. If you can use a location near to a protecting wall which is south facing, you can select a wider range of Poncirus and Ichangensis hybrids. In Addition to that slight winterprotection is much easier to fix. To explain see the following pictures of my Citrus-Spalier (sorry do not know the english term)
On this side I am growing Trifolis, Rusk Citrange, Ichangesis, Hybrid US 119 and Morton Citrange).
The plants are growing much stronger with no limitation of the roots, so it is advsed to plant them not as close as I did.
My personal favorite and really hardy Poncirus Hybrid for unprotected area is the Swingel citrumelo. As c. paradisi as one of the crossing partners which needs lots of heat during growing season, it should be the best selection for you (only ornamental).
Below see my 13 Year old Swingle which set on blossoms last year the first time ...
If you expect ripe, edible fruits Yuzu might be best selection. If got various other hardy crossings under testing periode, but for most of them it is to early to judge.
Best regards from Hamburg
Andi
http://www.zitrusgarten.net