I've been dealing with a slow Outlook 2007 for about a year now. By slow, here's what I mean: when clicking on Send/Receive, the process takes perhaps 4-5 minutes to download 75 messages totalling about 400k. I have high speed internet, and have spent much time troubleshooting Outlook. My PST file size is 300MB, not large by any means.
Looking online, I found several people touting the virtues of: reducing pst file size, turning off RSS feeds, turning off add-ins, compacting, cleaning, updating service packs, autotuninglevel, safe mode, or turn off indexing, but none of these did anything to help my problem.
What did solve my problem? The skinny answer? Delete Sent Items. I send lots of attachments, mostly pdf documents, or photos. By getting rid of any e-mails in the sent items folder that were larger than 500k, Outlook immediately sped up. Now the approx 75 messages at approximately 400k takes 15 seconds!! That's a healthy improvement.
Now, I just archive the sent folder once in a while, or I delete sent items with attachments, and outlook is very happy.