I don't think there would be a major difference within the context of what we're discussing; they're both coldwater species which can withstand wildly varying fluxuations in water temperature -- so we need to go on that premise and figure out which cat would go in these kinds of waters, if any can at all...
Ok, fair enough. First of all lets clarify the coldwater species part, if goldfish are goldfish, they are not a coldwater species. While goldfish will tolerate cold temperatures (some people here leave them out over the winter in the horse trough or pond all winter long), they are not truly a coldwater species like trout, or salmon, or arctic grayling. No goldfish or catfish are found in cold or arctic mountain waters to my knowledge. So what you're looking for is a catfish species that will tolerate colder temperatures.
Second, lets talk size; goldfish get big. Many people don't get that - your common feeder goldfish for example, will grow to over 18" in the proper environment, and I assume therefore that your fancytail goldfish will as well. So you also need a catfish species that will grow in size along with your goldfish.
Third, lets talk purpose; you stated that you wanted some fish to clean up the gunk on the bottom and possiblely the glass of your aquarium. The only glass cleaning catfish to my knowledge is a pleco. The common pleco will grow to size with your catfish (provided they don't get too huge, which they shouldn't in your 60gal aquarium), and I have kept plecos in a unheated tank - although I don't know that that is necessarily recommended (as they are more tropical). And you do realize that goldfish themselves are a bottom feeder right? If you want them to help clean up the gunk, minimize feeding or feed shrimp pellets rather than flake food. Part of why goldfish tanks are seldom crystal clear is because the goldfish are stirring around in the substrate. Its part of why goldfish and trout can't coexist in the same pond.
Keep in mind that most catfish you see for sale in a pet store are going to be like most of the fish - i.e. tropical. If you want to get something more tolerant of colder temperatures that will grow in size with your goldfish, you'll probably need to think outside the box (i.e. my recommendation of a channel catfish, which you're not to likely to see for sale in many petstores any more - at one time albino Channel cats were fairly easy to get).
And lastly, identify for us what temp. you plan on keeping your tank around. When you say coldwater, I picture my native trout tank that has a chiller on it. I presume from reading through some of your threads and posts that that isn't really what you intend. But maybe you're thinking unheated or minimal temp. like 72 (FYI, some research indicates that goldfish actually do best in tanks that are allowed to experience normal seasonal-like fluctuations in temperature).
There are lots of different ways to do the aquarium thing as Taylor said, so decide on some of the specifics, then go from there.
Hope that helps.