This is a very small, but usefull script for 3ds Max. It can increase the performance of the viewport by showing all objects in the scene as a box, except the selected objects. So you can see the selected objects normally and you can work on it.
Version: 3ds Max 9 or later
Installing: Unpack the zip archive, and drag & drop "displayasbox.mzp" file to your max viewport. Go to "Costumize User Interface", switch to "Toolbars" tab, select "Main UI" group, select "Heavenly Pictures" category, and drag & drop the "DisplayAsBox" icon to your max toolbar.