While I am not in your area, I think the winters are about the same. My SIL has had 2 large pots of ivy for about 4 years, that live out, under the slight shelter of a tree and an overhang - she waters them as needed. While the leaves on one go bronze-y for the winter, both pots are trained over forms and are trailing down about 3' over the edges of the container. She plans on using variegated ivy in 4 hanging baskets, from the front of the garage/tack room as decoration this winter - the house is on the market, and needs some decoration outside. If it gets REALLY cold - below 12 or 15 deg., then she brings them into the tack room overnight. If you do the same with yours - using your garage or an enclosed porch instead of the tack room - I would think they would be fine.

I know the various ivies do fine in the ground - it's only the extra cold the roots would get from being in pots that you need to worry about. Double pots, with the outside one bigger than the inside one by 2-3", and the space between filled with straw, leaves, mulch or even styrofoam peanuts would also protect the roots.

I am in upstate SC and have left my ivy topiaries outside all year long for several years. In the winter the tips turn a pretty shade of burgundy.