Separate retention category policies for journal & user archives

I see in 10.0.3 you can apply a separate policy to the journal mailbox.  It would appear (as long as your archives are in separate vault store groups) that this would allow me to put different policies in place.  We have never enabled storage expiry and would like to have that start happening on the user archives but have the journal archive never delete anything.  Has anyone done this or have any best practice tips they can offer?

Thanks