FCPX vs AMD compatibility

Hi, I would like to know if with the latest version fcpx, in my mac I would like to install a 4gb AMD RX 480 for editing video in 4K with native files or even converting to prores if needed, but 4gb of vram is enough? or is 8gb better?The problem is that used video cards amd 480 or 580 from 4gb on ebay are decent prices, while from 8gb the prices are very high unfortunately, I am not a video professional, but an advanced amateur, so what do you advise me?thank you.

Which computer? Which OS are you using? 4 GB should be enough for most editing. 8 is better. 

Mac pro 2010 OS Catalina.

This is the list of supported after market cards

support.apple.com/en-us/HT202239

The MacPro 2010 can only go to Mojave with a Metal capable graphics card.

Thanks for your advice, I want to try to work with native H264 4K 3840x 2160 files and see if the gpu with 4gb works well, otherwise instead of buying an 8gb rx which costs too much for me, I prefer to convert h264 4k 3840x2160 files to prores with fcpx directly, and I shouldn't have any problems right?
good day.

ProRes needs big, fast hard drives, especially in 4K. You might be better off working with ProRes proxy files.