I have discovered the reason for poor performance in X-Plane 11.
The reason in simple it is because FlyinsideXP is primarily a single threaded process it is using mostly only a single core and this can be verified in MSI Afterburner with all but one core at idle.
I couldn't figure out why when displaying performance mode in the Oculus tray tool I was getting a high unused performance but it was dropping frames like crazy.
It because it's running on a single thread and is not multi thread optimized.
Hopefully in future updates it will be fixed.