Laggy transitions and laggy 4k compressed videos in TImeline

Hello guys,
I've built my Hackintosh recently in order to use Final Cut Pro.
On my work I'm using Mac Mini with M1, I'm not satisfied with the performance, especially the rendering.
My colleague has iMac, I'm not quite sure which exactly but it is with Vega 64, 64 ram, etc. - quite well.
However on both computers the FCP isn't working as smooth as I was expecting.
The transitions are quite laggy on both machines.
The MacMini handles better the ultra compressed 4k videos from StoryBlocks which we're using.
The iMac and my Hackintosh are slower on those videos it takes time to start the preview and they're always laggy.

My configuration is as follows:
• Z390 AORUS Master
• i9-9900k
• RX 580
• 970 Evo Plus

I previously had Nvidia Asus 2070, but I had to remove it in order to build a Hackintosh.
Is it going to be worth to upgrade RX 580 to 5700 XT?
Is this going to fix the transition lag, the loading time of the compressed videos in my timeline, etc. or in other words is it going to improve the performance?I don't want to waste money and have zero results.
On the Bruce X test I got around 9-10 seconds, so does the MacMini but in 15 minutes video in 4k, my Hackintosh handles it for 10 minutes, and the Mini 20+.
I'm considering a Hackintosh build in my office if it is going to be worth it with better video..

What specific transitions are you using? They're not all built equal.