Hmm. Not exactly easy to do I think. Restricted Software works on the process name not on a version. The only way I can think to do this would be use the path to the executable in the process to watch for, but that would mean it could be pretty easily bypassed. What I mean is, instead of putting in something like "Microsoft Outlook" as the process to watch for, put in:
"/Applications/Microsoft Office 2011/Microsoft"
I haven't tested this, but I think that should catch instances of any applications running from that directory and shut them down, whereas it will ignore anything like:
"/Applications/Microsoft Outlook" etc.

Again, complete untested speculation on my part. Put that in and scope it to a single test Mac with both suites installed and try it out to see.

You may have already worked this direction, but have you thought about smart grouping your Outlook 2011 clients and sending them a message to get themselves migrated over? Or even use the same smart group to remove the outlook 2011 app but retain the data? I am not sure how your shop approaches this type of migration but this is a possible alternative path.

OK,
So a bit of sideways thinking solved this
A script to rename the Microsoft Outlook 2011 app to OldOutlook.app located in /Applications/Microsoft Office 2011/
Then create the restriction policy on the OldOutlook.App

Bish Bash Bosh sorted!!

I'd be more brutal about it. Just run an uninstaller. It wipes 2011 completely from the machine.

That's what we've been doing.