I had a client experiencing very slow performance when ever opening a library using the Open with Explorer option.
Lots of posts regarding slow performance in regards to opening libraries using Windows Explorer seem to focus on different registry settings or GUI editable network settings.
Now, the library had only around 900 folders, with a view that was sorted alphabetically ascending on the title column.
In this case, however, the solution was simple. I created an index on the title column, waited a few minutes, and that was it.
Now their employees are experiencing a blasting performance when opening their document library, and the CTO is smiling a whole lot more.