Output Connection Choices Make a difference
I'm currently building a large awards show which requires multiple outputs for various screens around the set. While trying to get a consistent output I've tried various ways of connecting the output from the computer to the LED processors and TV feeds.
I've managed to contain the project down to 4x 1080 outputs in our Hackintosh rack mount computer. The computer has 2 GPUs installed (GTX680 2GB/8800GT 512MB) and we have both a Datapath X4 and a Triplehead2Go so there are plenty of options to try.
What I've found interesting is the variance in FPS depending on how you output to screens. This isn't a complaint, I'm just sharing my experiences for others to see.
Bottom line - always try to output from Millumin via the primary GFX card. When using a second card it just adds processing to the output.
In my tests if I use a combination of the Datapath and Triplehead2Go I can get 60fps playing multiple compositions @ 7680x1080. When instead using a 2nd card for output (along with the datapath via the primary GPU) a 7680x1080 project dropped to 20fps for the same playback.
One thing I can say though - newer GTX GPUs now support 4 outputs (it used to be 3 max) so its not difficult to get multiple outputs from the MacPro or Hackintosh.