Its cool that you are getting back into the 11r, it is truly a great piece of gear.

Something you may find interesting is that the 11r is no longer run as an instance (plug-in) inside the protools architecture. Instead, avid has released a stand-alone 'eleven rack editor' that runs outside of (and concurrently with) protools, the bad news here is that it only works with 11r version 2.x (this is the 11r 'expansion pack'), version 1.x won't work for anything that is currently supported by avid. So, you really should find a way to upgrade to the expansion pack, I am running version 2.0.1 and I think that is the most current. Plus, the new cabs in that version are awesome.

The good news is that the 11r will work with just about any daw, that's assuming you get the expansion pack working and download the FREE avid eleven rack editor. For my setup, I have protools 12.5 on a 10.11.6 mac mini that runs pretty well, but most of the time I prefer to use the 11r in Logic Pro, and I have also tracked sessions in Reaper (free version on windows) and Cubase with no problems.

I don't think the OS version you choose will be as limiting as the 11r will be without the expansion pack update..