mIRC already does this. That is what the fast update feature was when it was available as an option in the display dialog. The option was removed and made permanent.
The issue is that when a large amount of information is being /echoed, mIRC has to update the display at some point. For example, if you run a script that /echos 10000 lines, at which point should mIRC display the text? The lines are being /echoed far faster than mIRC can update the display. Should mIRC just display the last page of text once the script finishes? The user would get no visual feedback that anything is happening until the script ends. Should it display a minimum of N lines per second? That number would depend on how powerful your CPU/GPU is.
Currently, mIRC updates the display reasonably often such that visual feedback is provided when displaying incoming lines, ie. the user can see the lines scrolling. That said, I think I can tweak it to update the display progressively less if a large number of lines are being /echoed in sequence.
Whether this would make any difference in the context you are describing, that is difficult to say.
