Success a new Hackintosh, but what to do with iGPU

This time i decided to build a hackintosh specifically for FCPX. The build itself is successful and recently I build exclusively on Asus mainboards, its my 5 or 6th built mac, all using Asus hardware.

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CPU Coffee Lake 8th generation Intel i7-8700 3.2 ghz,

RAM 24 GB DDR4

ASUS Prime H310M-K LGA1151 (300 Series) mainboard

500 W power supply

Samsung 1TB and 512 gb SSD drives, 1 7200 rpm 4TB drive

Video card Asus RX580 8GB (replaced earlier model Asus RX560 2GB)

Internal GPU: disabled in BIOS

CMBIOS iMacPro 1.1 2017

Kexts: Whatevergreen, Lilu, VirtualSMC, Intel Ethernet driver

Clover bootloader (was version 5107).

OS Catalina 10.15.4

Sound output through Sony ECM-PCV80U USB card with 3.5mm input and output

Mike USB Marantz PMP1000U

Display 24 inch Dell

The computer is used for FCPX 10.4.8, some graphic work, Apple Motion and Compressor. I don't use BT, wifi on the build (so no card for them). I already did a couple of videos on the computer. Everything works, fast. VideoPROC shows that both HEVC and H264 have hardware acceleration, though it doesn't specifically name the video card (Video card N/A). I have normal sleep, wakeup etc on the computer.

Here are my questions.

1. Asus RX 580 is supposed to be natively supported in Catalina. But I found that Whatevergreen and Lilu are still needed (in EFI, kexts, Other). I don't understand why? Can I take both kexts out of the EFI?
2. I disabled the internal Intel GPU completely because I think that RX580 is at least by 10-20% faster than the Intel CPU. However, I had a couple of crashes in FCPX under large load, which made me reboot computer completely. I finished the video exporting, but the issue made me think about the role of internal GPU. This thread says "iMacPro1,1. IGPU should be disabled to fully utilize the AMD GPUs encoders. Final Cut by the way works just fine for me. The reason the Radeon VII isn't utilized in iMac18,3; 19,1; 19,2 SMBIOSes is because they all use IGPUs for the encoding" - thats why I use iMacPro now, to utilize the speed of RX580 fullt. However, by effectively disabling internal GPU I basically lose one of 2 graphic cards (external and internal) available, while in theory both cards could work like in Internal GPU+eGPU (rx580) mode.

The question is, should I use SMBiOS iMac 19.2 or other definition to use iGPU, turn on internal GPU in bios, and reuse it in tandem with the RX580. Will give it any benefits in FCPX work? Or will it slow down?

Thanks beforehand!