Significant delay when moving mail

Exchange/Outlook – Having intermittent problems delays of over 30 seconds when moving emails from Inbox (server) to personal PST (also a network drive). Offered Remote Assistance and checked his folder. Found that his Personal PST is 866 MG. Advised user to create several PSTs and move the emails to those newly created PSTs.

Other than monitor his workstation and server, what else is there to do.