Those are pretty small trees. I live in the area as well, and part of my strategy was to grow the marginally hardy varieties in a greenhouse and let them get to a certain size before planting them to endure winter conditions. Somewhere, I had heard of a "rule of thumb", that the lower part of the trunk should have the thickness of a human thumb before being exposed to frosty weather.
Another consideration for varieties on the edge of their cold tolerance would be rootstock vs. own roots. I was going to try Yuzu on its own roots, and others as well, so that if the top dies back completely, it could regrow from the roots as the same variety. OTOH, grafting to a Poncirus rootstock like Flying Dragon might make a good tree as well and maybe help with cold tolerance of the scion. I couldn't decide which was more important, so I'm doing both, at least for Yuzu.