MAC Performance Getting Slower

I am a PRO user of unity for years now and have been writing an RPG game for the last year and have diligently updated my unity version through the 4 to 5 releases. Due to being in a development cycle which is not close to production yet I have had the luxury of putting unity through its paces a lot. The work I do is not GI Enlighten based because my game is purely dynamic procedural world building. I am targeting standalone platforms which are Windows and Mac but i am getting huge performance swings post 5.2 unity versions regarding deployment to the Mac Pro Mid 2015.

My latest game build which can be accessed from www.virtuoso-life.com has two installs Windows/Mac but my user base is really complaining at how horrid the mac performance is. Here are some empirical stats taken by the users recently.

Medieval Docks Parcel Windows (7,8,10) Users Averaging [52 - 80fps, NVidia 600 - 960 Cards]
Mac Users (Yosemite & Capitan) Users Averaging [12 - 24fps, Mac Pros (2014, mid 2015s)]

Virtuoso Arc Parcel Windows (7,8,10) Users Averaging [60 - 105fps, NVidia 600 - 960 Cards]
Mac Users (Yosemite & Capitan) Users Averaging [15 - 28fps, Mac Pros (2014, mid 2015s)]

The mac builds are experiencing nasty GUI flickering with the new GUI system where when you close a panel it flickers with some kind of atlas showing behind.

I am at a loss why the mac is performing so badly and the windows platforms are performing so good. I've tried all quality settings. I've tried stripping out the water, the drawing of trees grass on the terrain with exactly the same relative performance issues as shown above.

I don't want to harp on about this anymore but this thread has become very hot indeed but after taking out all the emotional content there does seem to be real issues with unity 5.3/5.4 deployments to macs. It is very difficult to package up these kind of performance issues and give to unity due to the extensive complexity of user game development but this issue REALLY does exist I think unity should look into this carefully. It may turn out to be an apple related issue but some more analysis and feedback would be much appreciated by this thread and community in general.