itch.io

I'm no expert here, but I believe the drop on fps is items on belts (in fact I had a very long belt that was so full of items it crashed my game) so ideally optimizing belts would solve that issue

edit: An I idea I've had to help remedy logistically issues is to let Inspector Panels filter what item they can see in an inventory in the same manner as Filter Funnels

You can already kinda sort the recipe book. If you click the empty heart box above the item descriptions, it adds the item to the favourites. Then you can click the heart button above the item list to view only favourites. The order in which you favourite items determines the order in which they are displayed.

When it comes to the fps thing. The game doesn't skip frames, but instead slows down when lagging, so I wouldn't have expected the lag to affect the logic. If you experience that the lag affects how the simulation unfolds, I would recommend that you try to reduce lag. Tigorahan is right that items on belts cause lag, so it is best to use long distance funnels or hands for transportation.