No longer guest as I just registered.   

I live in Burlington, Ontario, Canada I have a 3 foot deep pond with about 50 Lionhead Goldfish that spend the summer and winter in the pond and have for the last 10 years. They have up to 6 inches of ice on their pond often from mid November until late March or early April. Some are as big as 8 inches long. They often have a bit of a hazy look first thing when the ice melts and they start to move about. Once the filter and the UV get started and the pond starts to warm they clear up and are just fine. They usually spawn the last week in April for the first time. The eggs have to be taken indoors to hatch as they do not hatch well in such cold water. In their pond I also keep Gold Dojos and Gold Medakas that have a substained population that also survive the winters.

I believe all goldfish can survive winters out of doors in most moderitly cold climates. Just Bubble Eyes and very long finned Veiled types may have problems. The biggest problem a fish has is being owned by a person that is too lazy to clean a pond properly to prepare for winter.

Every winterI keep several hundred small koi and lionheads in a above ground  pond constructed with 12" planks with a liner. A plastic greenhouse style frame is set over it and with only an air stone in one corner they make it 99%. The ice that forms inside on below zero cold nights and days is never more than an inch.