First, I can't attach the new patch to the old report because sf.net is broken (doesn't allow users to attach files unless they own the report! blah) Sorry about that!
I've updated the patch to be just a bit more efficient! Now using the SCN_MODIFIED notification when text is added or removed. Also, only updating the width when the line count increases or decreases exponentially. That means, it's updated after lines 1, 10, 100, 1000, 10000 ... etc.
I'm not sure what happens after the gint overflows at line 10,000,000,000 ... ;)