Setting eM Client to download content and attachments for offline use may speed things up after the initial download. Of course if you have a slow connection, that will probably not make much difference.
If you have set eM Client to download content and attachments for offline use, then the problem with clearing eM Client’s cache is that it will have to download all that content again.
Thanks! I noticed that it is mainly me Yahoo mail that is sluggish. Since i also use some maps on topics there i just set it to “Offline Use”. I hope it helps. Outlook goes like a charm, speedwise.