Something like that would take a long time regardless of how you formatted it. It would also get very large no matter how you format it. You are better off using Windows' search function to search for text in files and just let it take its time through the logs. You can cut down on log size by stripping control codes as well.
Or, if you know that you don't want to search text from specific people (such as bots) or that include specific information (such as ads), then you can write your own logging script that will not include those things in the logs. That would also cut down on the log sizes.
Regardless what you're looking for, using mIRC to do it would just be slow and the database file (whatever one you use) would be large as well when you're going back that far.
