well, I can't say that I'm surprised that there's a noticeable spike in CPU resource use, given that your nick colors are trying to cover whatever settings you have them set for over 4000 nicks, and in addition to what ever other programs that you're using.
How much RAM do you have? How much free space on your hard drive?
The fact that the levels only appear in one channel, is, for the most part, irrelevant, as mIRC doesn't know this, so it monitors all of the channels that you're in for matches.
This, in my opinion, isn't a mIRC bug, but rather an extensive use of the options available in mIRC that require constant updating, and, therefore must be run from RAM, rather than being able to store the information in a file on the hard drive.
Technically, I suppose, the information could be stored on the hard drive, but I think you'd probably find a bigger lag than you currently do, as the hard drive would have to be accessed every time there's a comparison needed to be done.
