GTX 680 and LG 4K monitor -> no 60Hz?

[mumux]

Hello,

So I have this new 4K monitor, the LG 27UK650, a nice monitor, but I'm not able to make it work at 60Hz.
The Mac Pro is a 3.1 with an Asus GTX 680 2Gb that I flashed months ago with the help of this post:
https://forums.macrumors.com/thread...-pci-e-2-0-5gt-s.1603260/page-4#post-17832428

The problem I'm experiencing is that if I set the monitor Displayport to 1.2 the Mac does not boot at all.
If Displayport 1.2 is disabled (working at 1.1 I guess) the Mac boots and of course I only get 30Hz.

I tried SwitchResX but 1080p @ 60Hz is not HiDPI (because of the Displayport setting).

Since both the GTX 680 and the monitor are supposed to work at 60Hz, what am I doing wrong?
Should I send the monitor back?

Thank you

 

[Fooze]

This might be a long shot, but have you tried any other display port cables? Maybe your cable is limiting the bandwidth.

 

[mumux]

The cable I used is the one included with the 4K monitor so I guess it should't be the culprit.

 

[Fooze]

That setup should work. I have an evga gtx680 and it’s working with a Dell 4k display.

By any chance do you have a Windows install you can boot into? See if it works there and then you’ll know it’s software issue and not hardware related.

 

[mumux]

I don't have a bootcamp install, just parallels, but I had the chance to try a friend's GTX 680 (MSI not flashed) and it worked fine at 60Hz.
No bootscreen until black screen with white apple (it's a High Sierra unsupported install) but I guess this is expected.

Then the cuprit seems to be the Mac ROM, any thoughts on that?

Thank you

 

[ActionableMango]

The main benefit of the MacEFI is boot screens. However, there's no way to get 4K boot screen out of a GTX 680 anyway, flashed or not. So you might as well restore your original firmware if that fixes your other problem.

 

[mumux]

4K boot screen worked @ 30Hz in my card.
In normal operation, with a correctly working MacEFI, I would use 60Hz, but if I need boot screen, I could just set the monitor to DP 1.1 and reboot!

That's why I'd rather try to make it work correctly than look for a 2ᴺᴰ card with boot screen.