I use similar folders extensively. In my work, I get many emails about the same projects all the time. For example, this week all my emails are about the same 6 projects.
I placed the "move to folder" icon on the Outlook toolbar. Click on it and get a list of about 10 of the last folders you've saved emails to. If you've been in and out of the same files all week, this is a big timesaver - the list is right there, no matter where you are storing the emails.
The keyboard shortcut is CTRL+SHIFT+V.
Alternatively, you can right click on an item and select "move to folder" and you will get the entire tree to choose from. Useful if you can't remember offhand where it is supposed to go.