Frederico

So it'll be cool if a 4,1 (flashed) or 5,1 Mac Pro (maybe even a SIP-disabled 3,1 running HS) can at least recognize this card, but with only PCIe 2.0 x16, it would seem that it will be bottlenecked. I might be wrong, but just like the 3,1  (even though it also has PCIe 2.0 16x) really only fully benefits from a GTX 960 or under before hitting a bottleneck,  if I've read things properly, the 5,1 is also a bottleneck for the 1080ti, so I suspect the same for at least the top Vega. I hope I'm wrong. 

I'm also seeing lots of PCIe 3.0 cards not properly negotiating in MP 2.0 slots, either downstepping to basic 1.0, or reducing lanes by half.  It is extremely frustrating to be artificially crippled with zero chance that Apple would work with a vendor to correct the issue on their end, let alone issue firmware for 5-7+ year old machines that otherwise remain viable workhorses awaiting a 2018-2019 rethought Mac Pro.