Hi Mathew,
We have one or two more things to check with regards to setting up our server in the strictest sense of "Database tier must have all the saved files and DB itself".
I am leaning more towards swapping around our VMs to give the App server the space to house all of the files and then just have the mySQL database on the Database tier.
At least I can site performance gains doing it this way, and besides, if the moodledata is encrypted at hardware level and the only way to tell which file is which is by hacking a firewall to mySQL on the database server, then I guess that is pretty secure.