Hi biobob,
I understand the inconvenience caused by this issue. Since the issue seems to be related to Outlook 2011 performance, I suggest you check if you install updates for Outlook 2011 to see if there is any improvement. You can click check for updates as below picture.
Moreover, please temporarily reduce the mailbox size(I suggest you enable personal archive, and put some emails into archive folder using a PC), and re-create a new identity for a test to see if it can narrow down the root cause of the issue.
Thanks,
Johnny Zhang