GTX660, 4K Iiyama - display issues

[kynleborg]

Hi,

 

this is my first post in here so please be gentle. I've tried to find the answer to my problem by searching, but with no luck.

 

I have a system identified as iMac14,2 - 4790K, Gryphon Z87, GTX660, set up using Clover.

It has been operating on 10.11 with no issues. I decided to update to 10.12 and again - no major problems (ALC892 wasn't working properly but managed to fix it).

But the the update to 10.12.1 has shown up and it got broken the display.

Worth mentioning - I haven't been using NVIDIA Web Drivers till now and 4K resolution was utilized properly.

 

Back to problems then.

The only resolution working fine is 1280x720:

When I switch to any other (including "No scaling" option) I get something like this:

 

Current setup in Clover is - inject Intel. When I switch to inject NVIDIA I'm getting the well known "black screen on boot" problem.

I don't have NVIDIA Web Drivers installed, but been trying to as well and the problem remained.

 

I'd like to ask for you help and advices.

Please also let me know if more info on my setup is needed.

 

PS. I know 4K doesn't work often, but I had it operating just fine. Only the latest update got it broken. Even 1920x1080 (4K scaled down 2x) is broken.