Bruce the colder the water the fish are in,, the less solids they will produce due to eating less food thus water changes would not have to be as frequent nor as much. As mentioned earlier I would try to have the water mostly above 50F-55F which will keep the biofilter active and the fish will feed a little better and that may result in a little fish growth or at least they will maintain good body condition over the winter.
Keeping it warmer will certainly be beneficial.
Certain types of biofilters, like fixed film, will run to about freezing, just that they can get very large. My cutoff is 55F for practical purposes.
The biofilter was originally developed for municipal waste water treatment in all climates. They make some pretty big ones. The use for fish came a bit later.
