That seems to be an issue with Bethesda games in general, up 'til now. I will notice the lag in FO3 and NV as well, with a "bag of holding" type container that I throw everything into. Part of it is probably related to what HeyYou mentioned, with items with attached scripts having said scripts start running when you open the container. I have always thought it was the inability of the game engine to handle the calculation changes associated with so many items in the container. The game engine might be set up to recalculate every time you click on another item in the inventory. It is just a theory on my part. With that said, even though my experiences are generally with the older games, both Fallout 4 and Skyrim (both 32 and 64 bit versions) are built using modified versions of the Gamebryo engine, so maybe the issue is game engine related. *shrugs*