Sleeper PC Building - Linux for HDR 4K UHD Playback - Recommendations?

Ventilation. Probably depends a bit on what hardware you land on, but that era of case wasn't exactly designed with airflow in mind.

If you just want Bluray ripping/playback any modern AMD APU should do the trick. Playback/ripping of media is a largely solved problem. Either it has the decoder/encoder built in and the CPU sits idle, or it doesn't and the CPU/GPU go crazy trying to play it back, and even longer encoding.

That said HDR sucks balls on basically everything but the highest end displays. HDR on a "conventional" IPS panel looks awful because it just cranks the brightness up to 100% and your blacks end up looking like greys thanks to IPS' mediocre contrast levels. IMO HDR is only worth it on OLED displays. Mini/micro LED displays with a TON of zones can look ok, but it needs to have at least quad digit dimming zones. According to google the MacBook pro has 2,554 dimming zones and it's display largely doesn't bother me. That's at only 16 inches.

I am doing a similar thing with a mid-level build in a Dell Dimension 4600 case for my daily driver, but going full deep-end.

My main hurdle right now is RAM. I'm trying to find a 2x16GB set of green RAM with no heat spreader. I happen to have a stinky-poo-poo set of 2x16Gb Samsung 2133 (unknown CAS, but likely terrible). I'd ideally like to have something typical like 3200CL16, but really the only thing I can currently find are all those CL22 sets by Crucial. Does anyone have any other ideas for RAM? I'm thinking of just picking up one of those Crucial sets, it's probably good enough and certainly better than whatever I've got now, but the fact that I can very easily get gamer-y RAM with lame heat-spreaders in exactly the capacity, speed, and CAS I want, but I can't get it in green... You always want what you can't have!

I have a single 80mm exhaust fan, and I've done some testing, and with the components I have (R5 5500 and RX5700XT), it's actually not as bad as I expected thermally, and suitably quiet. I am waiting for some more Be-quiet 80mm fans to come in to put one in the front, and also possibly on a hole I have yet to drill in the side-panel...