First off, you'd need to determine the number of characters in each line, and then total them, so actually counting the number of lines is (next to, if not completely) useless.
Secondly: The 64k limit that you're referring to, isn't a literal file size limit, but rather the limit of the file size that can be edited using the Remote Editor.
Remote files can be created/edited using any text editor, as long as it's saved in DOS Text format (this is the default for programs like Notepad).
Files that are bigger than 64k can be loaded and used in mIRC, they just can't be edited using the Remote Editor without creating problems.
