I open a 53MB text file. In the Global Options I have requested to ask me what to do with large file, but no dialog pops up. Instead, jEdit immediately starts loading the file, and remains irresponsive for about 2 minutes.
If it's already a text file, then the dialog should not be the same -
because your choice then should only be related to whether you want to disable word wrap.
The other choice (disable or partial syntax highlighting) don't apply for text files!