May not directly relate to your post, but I gave up on Outlook a few months ago. It seems to be doing too many things "internally" which are of no consequence to us. Why should a simple mail client keep so busy I wonder. And to top it all, its a back-door for those viruses and bots to get through into your PC!!
I switched to Eudora which is also free and is streets ahead of Outlook in every sense. MS just used their unfair advantage to promote Outlook's use. Get Eudora from qualcomm.com and you won't need to bother . . maybe that solves the speed problem as well.