I think ChatGPT just helped me figure out a potential performance issue and also came up with a better high performance solution. 
This will also allow for more dynamic search.
It will require a bit of refactoring, I'll try to adapt this as soon as possible.
For now I have added a hidden max item setting in 5.377 (run while BTT is quit):
defaults write com.hegenberg.BetterTouchTool BTTNumberOfItemsToKeepInHistory 1000
Note: items are only deleted on BTT startup (regardless of days or number setting)