dual gpu

Hi, After a long journey I managed to get my upgraded MacPro 4,1 to 5,1 to run Windows 10 and Mojave 10.14.4. which are installed on partitions on the same SSD, so I'm trying to dual boot. With the RX590 there is no bootscreen, but the mac will boot into Mojave. Now the thing is I've messed up...

I recently purchased a GTX 285 flashed with the mac EFI as an upgrade to the 5770 in my 2008 Mac Pro running OS X 10.11.6, the dilemma is the GTX 285 only supports Legacy OpenGL (2.1 and earlier) while the 5770 supports OpenGL 3.2 This isn't a problem as I can just run both at the same time...

With no other viable options at the time, I made the following upgrades to a 2010 Mac Pro (5,1) about two years ago - primarily for rendering with VRay. VRay uses CUDA, so the AMD GPUs of the trashcan Mac were of little use and adding Thunderbolt chassis for external GPUs would have just added...

So I recently upgraded to two Flashed MSI Twin Frozr R9 280x's in my 2010 Mac Pro from a single OEM 5870. I was mainly looking to improve render and export times in FCPX, and I went with Dual R9's because the chip architecture in the R9 280x is very similar to the D700 Firepros in the nMP...