I know that the R4E has 4 x PCIe slots. Do you know if it is possible to setup more than 2 GPUs? Specifically I am thinking about trying to put in an AMD R9 280x as primary card for dual monitors because it seems FCPx likes AMD more. Then I was thinking about putting two GTX 760s in as well to get added boost for my other apps that like Nvidia. Is it even possible to mix and match GPUs? And to have 3?