Currently, when jEdit is given a large file to open (either during runtime or on startup, e.g. when the perspective.xml file specifies a large file), it may take a very long time, during which jEdit is not responsive. jEdit should catch this (like firefox realizing that a slow script is running) and ask what to do - cancel the loading of the file, or maybe other things.
The criteria of file size is not good enough. Two files with the same size can take a very different time for loading.