RX580 requires RadeonDeInit=true graphics option to be set in the config.plist. Do not set any other graphics options, especially with your IGPU-less CPU (i5-9400F). You must have WhateverGreen.kext installed to your bootloader's kext folder along with Lilu.kext. You should be using a SMBIOS that only has a discrete GPU such s the iMac Pro 1,1 or Mac Pro 7,1.
Using the defaults from Unibeast is unlikely to include this essential graphics option, it needs to be selected manually.
The 5750 is natively supported since Snow Leopard, it will boot your system without any config.plist settings, may not have full acceleration without a few tweaks but it will not boot to a black screen like the RX580..
Having a fast SSD, RAM, CPU and motherboard doesn't equate to a fast booting system. Because you can easily miss out essential settings or add in wrong settings, kext and drivers to your Clover or OpenCore folder that cause the boot process to halt or take longer to complete. USER ERROR not issues with the components are more likely to be the cause of the slow boot.
Getting macOS to boot on a Hack is only the start of a journey, the hardest part is getting the system to work at its optimum level.