OpenCore - Mojave 10.4.6 - ASUS Prime Z370-a II - RX 580 image / resolution issue

Hardware: CPU: Intel 8700k stock

GPU: Sapphire Nitro+ RX 580 8GB SE

RAM: 32 GB (2x16 2666) Patriot Viper

Motherboard/Laptop model: ASUS Prime z370-a II

Ethernet Card: MOBO

Wifi/BT Card: N/A

Display1: AOC U2879VF 28" 4k (via RX 580 DisplayPort)

Display2: BENQ GW2250HM 21" 1080p (via RX 580 HDMI)

Guide: OpenCore Vanilla guide [https://khronokernel-2.gitbook.io/opencore-vanilla-desktop-guide/]

EFI folder: [https://www.dropbox.com/s/edzzhkhrz8qwnj7/Screenshot%202020-01-31%20at%2013.07.38.png?dl=0] [https://www.dropbox.com/sh/0jdt4ggqrhr48is/AACtU45NwtEeyagF7ae7aUYwa?dl=0]

Having spent quite some time researching parts for this build, aiming for decent mid-range power (audio production + light video work) with maximum OTB compatibility... It has not been an easy journey over the last few days.

After following the OC Vanilla guide and going round in circles stressing over the ACPIs, DeviceProperties and Platforminfo, the majority of my troubles seemed to have stemmed from my display configuration (BIOS and config.plist).

My BIOS is currently configured to preference the GPU, but have the iGPU on for multi-monitor support (afaik this is important for FCPX if I want to get the most out of the GPU and the on board for both hardware accelerated rendering and scrubbing etc?)

My smbios is set to 19,2. My Deviceproperties is set the the Coffee Lake one where nothing is plugged in to the iGPU

MAIN ISSUES:

1. My 4k display outputs black except when set to one particular resolution: 2560x1440 (low resolution). Anything else and it remains black (but not without a signal), and the other screen flashes on and off periodically. Both are detected perfectly in Display preferences, and also via screensharing.

2. When booting, neither display gets a signal until after the OC bootpicker. I had installed via a different display setup (HDMI only via the iGPU) as this was the only way I could see all the output on the screen.

Any help would be much appreciated! Also, any input on smbios (I've read so much conflicted information), and optimum hardware acceleration would be fantastic. i.e., what should I ideally see in the VideoProc settings page? (currently this: [https://www.dropbox.com/s/fimiw75yi61b970/Screen%20Shot%202020-01-31%20at%201.26.55%20pm.png?dl=0])

Thanks to anyone in advance! I will update any info if I've forgotten anything!