For those interested, as I generally haven't seen it this quick for others - it only took 3 business days for my Oath Certificate to arrive in the mail. Oath on Tuesday, case closed Wednesday, Certificate in mailbox Friday. Scarborough office.
The only advice I can give is to follow the instructions exactly in the Oath letter for the signature required immediately after the oath. Indicate the correct subject-line, and in my case, I added the Clerk's name in the Body of the email. During the Oath registration, I was told to note down the clerk's name, but wasn't told why, unless I missed it, so I just included it in my email.
Finally, as others have done, prep the form+signature ahead of time, so you can email the post-oath document within a few minutes of the ceremony ending. I got mine in around 2:45PM, in hopes that it would be processed before close of business...it seems I made the cut.
Hope this helps....now on to the final madness of getting a passport!