Well, I certainly made some assumptions about your workload that may not be true. What do you use it for?
As bulk storage (backups, media streaming, etc), random 4k reads are usually not going to be the limiting factor, except maybe for the occasional indexing by Plex etc. If you’ve instead got lots of small files you’re accessing, or are hosting something like a busy database/web server on here, then you could see significant boost, but not anywhere near as significant as just co-locating the service and the data. If your workload involves a lot of writes, then I would stay away. The MTTF on “cacheless” SSDs is pretty garbage, which seems like the biggest issue to me.
Also, didn’t mean to suggest buying nicer drives, just using an older one I was familiar with as reference. I recently bought the 2TB 970 evo plus on sale for $80 each, which was in your price range, but not sure if that pricing made it to the UK.
I don’t know about a guide, but I believe it’s still possible to rip 4K HDR using an HDCP downconverter . HDR/DV data is included over HDMI, the problem is that it’s all encrypted (along with the 4k stream itself) with HDCP 2 which isn’t publicly broken yet. This box (and others like HDfury) does some tricks to force a fall back to HDCP 1, which has been broken for a long time, so you should then just need a capture card that supports it.
Scene releases may have better/faster techniques depending on the streaming platform, but they probably wouldn’t talk about them if they did.