I have had the same discussion with my clay club up here is Washington. We concluded that the question is about how porous your work is when it is completed. If fully vitrified and non-porous (so some extent all ceramic is porous) the better it will survive freezing temps. It all has to do with the moisture that is trapped in the ceramic. When ice is formed in these areas it will crack the ceramic.
Not sure testing in a freezer would work, because it needs all the environment variables present in something outdoors.