I find that text editors can be surprisingly poor at opening GPX files. Many just aren't designed with large files in mind, and become unbearably slow if fed a megabyte of XML. If it decides to render the file as a single line (depending on how it's configured to handle line endings), you have to do additional scrolling around before you get to something meaningful like a timestamp or lat/long. Something that's designed for editing XML would be less painful.
On my (admittedly Linux) desktop, I've associated GPX with Viking, which is quick to start and renders them on a map.