@matthewpomar look in to VEGA cards or wait for nvidia to update drivers or new gpu gen to come out.
MVC is the only way to get boot display but he will be waiting for the same driver as you.
so a Vega 56 may be what you want to look in to, you will have to do the research
or just try a RX 580, if your not doing any GPU tasks then i dont see why a pulse RX 580 8gb cant drive a desktop.
@choreo
1- yes but you may have to get some dongle's to match the display outs to the gpu.
(this is a link to the one im using, different brand)
http://www.sapphiretech.com/productdetial.asp?lang=eng&pid=77B48A1E-9FCB-4F19-BC2D-17C3087E4852
1 x DVI-D
2 x HDMI
2 x DisplayPort 1.4
you can drive a max of 4 displays i think (iv only had 3 plugged in at once)
2- the RX 580 will work on osx 10.12 (Sierra) but it works better in osx10.13.
it will work in osx Sierra but there may be some bugs (vary few i think)
do check application compatibility
3- there is no easy way to get boot display, keep one of your old cards (but check osx compatibility as osx10.14 is drooping support for some of the old ones)
ie no boot display with any new card, i dont see the problem.
4- brand of card
5- less power id gess card seem's to use 30w when not used and 150w using luxmark to stress it.
in normal use working in davinci resolve i think it's sub 100w most the time
just checked about 60w when playing back video graded with some effects
i did change the bios a tad and the fans are fairly quiet,
if OWC provide support for the GPU they sell for OSX and your using the card for professional use then there worth looking at.
i got a used card for 1/3 that but there's no support or warranty but if i have problems im wasting time fixing it so there is value id OWC provide support
o and one RX 580 will be faster than the dual card setup
ps if you buy from OWC check it comes with power cables
i got mine used on ebay cheep so i had to order the power cables too
https://eshop.macsales.com/item/GIGABYTE/MP1012R580V/
found it, the bundle one has the correct power cables and has different ports to the one i linked.
do check to see if they provide support or not for use in osx as it is only a PC card and they are charging extra over say amazon but if they give support then for pro use it ma be worth it.
i got mine on ebay for £120 and paid £6 for the power cables (but no support or warranty)
edt
i dont know if drivers for nvidia are out but if so you can look at MVC for boot display on newer nvidia cards but in general AMD is better in osx unless you need CUDA
