Catalina - Flickering lines/artifacts with Sapphire 5600 XT

Hi all - I'm having issues with flickering lines that go all the way across the screen. On the desktop they are always within a couple centimeters of the mouse cursor. In some games they show up anywhere on the screen. I've been unable to find solutions.

Hardware acceleration seems to be working (CPU is almost idle and GPU usage goes up to about 25% when playing 4k H.265). Geekbench scores are only about half of what their tables list.

System:

Z170 Sabertooth, i7-6700K

Sapphire Radeon 5600 XT

Running Catalina 10.15.7

Some relevant stuff in my clover configuration:

iMac 17,1 (Is this appropriate? Would iMacPro 1,1 be better?)

boot options include agdpmod=pikera

Inject ATI is disabled

AddHDMI is enabled (I'm using HDMI)

kexts: AppleALC, FakePCIID_XHCIMux, FakePCIID, IntelMausiEthernet, Lilu, RealtekRTL8111, SMCProcessor, SMCSuperIO, USBInjectAll, VirtualSMC, WhateverGreen

VDA Decoder (as reported in HackinTool): Fully supported

I'm pretty much at a loss as to what else to try. I'm about to switch to displayport connection to see if that helps (I don't have a cable right now, that's why I haven't already tried). Thanks for any suggestions.

submitted by /u/threwaway747
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