Thanks guys, followed Graeme's advice and set the encoding under Languages->File Extension Manager for all extensions and that's working for me. I don't think I've encountered a non UTF-8 file since about 2008. Every other editor I use defaults to UTF-8, only slickedit has its defaults set to do something else.
Dan's advice is exactly what I was trying to avoid because that path is what I've been putting up with for years. First open the file, find out the encoding is wrong, close the file, manually reopen in the classic dialog and manually set the encoding. That path is not very fun.