Here's a capture card review ( Live Gamer 4K ) supporting 240Mbs or 30 MBs bitrate at 2160p60 footage.
The review stresses the requirements for a powerful cpu and video card but doesn't mention the hdd I presume because the capture card does that work ( saving the stream ). If one were using software capture, all hdd/sdd since christ was a child can read and write faster than that.
Just buy a modern large enough ssd. It seems quality depends on other factors liked codec, hardware, colour depth, etc..
https://venturebeat.com/2018/06/27/avermedia-live-gamer-4k-vs-elgato-4k60-pro-the-4k-capture-card-showdown/