1080p Scaling on Thunderbolt Displays with new mac pro SwitchResX

I just upgraded to 3 Thunderbolt displays for my new mac pro.

I really hate working in 2560 x 1440.

With my rMBP 13, the retina scaling is perfect... I really assumed this would be a no brainer on the Thunderbolt displays to "Retina" scale the displays to 1080p.

I was able to turn on the default HiDPI modes via the terminal, but all I'm able to select is 720p HiDPI...

There have been people who have successfully done this with the app SwitchResX, but it seems like only with Intel / Nvidia cards.

See related post: http://forums.macrumors.com/showthread.php?t=1568657

I am wondering if anyone has made this happen with the nMP Late 2013... as they have AMD GPUs.

I know OSX is capable of this it's really just about it being enabled... so why not?

Any one know what I don't?