Random crashes and performance issues running multiple graphics cards

[-VoiceOfReason-]

Hi all,

I have a 4,1 -> 5,1 flashed Mac Pro running High Sierra 10.13.4 (17E199). Here's what I am trying to accomplish:

* Run 3 27" Apple Cinema Displays via DisplayPort
* Have at least one monitor show boot screen for FileVault

Currently I have two monitors being driven by a stock Apple HD 5870. When I add a third monitor, no matter what video card I use, I experience the following:

* WindowServer will randomly crash and log me out of my session
* Any kind of GPU accelerated load slows to a crawl. Google Maps in a browser is basically unusable.

Here are the graphics cards at my disposal:

* GTX 680 (flashed for boot screens, one DP)
* GT 120 (stock Apple, one mDP)
* HD 5870 (stock Apple, two mDP)
* NVS 510 (stock, no boot screens, four mDP)

What could be causing this? Is this a power issue?

 

[bookemdano]

Bunch of posts on this already. Doesn't appear to like 2+ vid cards when one of them has an EFI. Not sure if the Mojave beta is affected--you might try it. I don't think there is any other solution other than taking out one of the cards or using two cards without an EFI.

 

[abdyfranco]

I have the same problem, too.

 

[ActionableMango]

Could just get a card with 3x DP and EFI like MVC GTX 960.