Re: POSIX subsystem
"Can't recall anything ever wrong with it? It outperformed Linux as an NFS Server last time I tested it!"
Seriously? Mate, if you are going to tout MS as being all greatness, at least pick something they are good at (along with a more believable quote about 'testing it').
Microsoft added an NFS server with two goals: POSIX compliance for contracts that required it and the hope of using it as a migration service for existing 'nix kit. Both of those reasons are nothing more than box-checking exercises. Microsoft already has SMB/CIFS, so NFS would seem to be little more than an afterthought.
Now the anecdote to reinforce that. A couple of years ago one of my colleagues bought a NAS box for using in our lab. This was a pretty typical vanilla 2U rack server from either Dell or HP (I forget which) running Windows Storage Server 2012 R2. I don't recall it being particularly cheap either, but we found it to be a reasonably capable iSCSI and SMB server, both of which were pretty straightforward to get going.
One day I needed some NFS shares for a project I was working on. We spent hours battling with NTFS permissions and the confusing NFS UI (not helped by the use of non-standard terminology) and eventually managed to get it working. The performance was pretty average at best, but sufficient to at least get on with things. Then we tried netbooting a box using an NFS share as the root filesystem, which simply refused to work.
After a few more hours not getting anywhere with that, we ended up wiping the entire OS and installing FreeNAS instead. Less than an hour later we had everything working perfectly (including SMB and iSCSI, plus much faster NFS) and simply got on with the rest of the project.
Microsoft has virtually no use case for NFS except to provide shares to 'nix boxes, and like you stated yourself the compatibility between the two isn't great so it's much less work to use a proper NFS implementation instead. I'm struggling to think of what possible use case it serves at all?