I think the beeps should be optional as well, or only beep the first few characters after the threshold.
Making mIRC beep only a few times after the threshold sounds like a good idea. I will see if I can implement that for the next version.
May I respectfully vote against this?
It is a good idea, except for one problem: audible alerts for only the first few post-threshold characters are going to result in users missing those alerts when other, louder Windows sound effects, mIRC scripting-triggered sound effects, or third party software sound effects coincide with and drown them out.
I find myself favoring argv0's general idea. The threshold beeps ought to be absent if "[ ] Enable sounds" is unchecked, and an "Editbox full" option could be added to the "On event, play sound:" dropdown. (Users could still have silent-except-for-threshold-beeps mIRC installations this way, just by checking "[ ] Enable sounds" and setting every event except for "Editbox full" to "No Sound". Or the reverse: leave all events set as is, and set "Editbox full" to "No Sound". Etc. And of course, with this, users could even customize the threshold sound effect.)
Just one forethought: if you do add an "Editbox full" sound event control, please consider, if it is set to "Beep" (as opposed to "No Sound" or to a custom sound), having said sound ignore the settings of "Event beep: Beeps: [___] Delay: [___]", and instead produce only one such beep per keystroke. Otherwise, typing would produce a racket.