This cheat sheet has everything you need to know when deciding on an Nvidia GPU for encoding HEVC. I would not recommend worrying too much about single vs dual encoders so much. Look at the columns for NVENC capabilities, they're listed in total FPS(@1080p) and total streams. This tells you how many FPS in total you will be able to encode with a given card, in something like Tdarr. For Plex, Jellyfin, etc take a look at the Transcoder Limits column. That will tell you approximately how many simultaneous transcodes you could be doing for all of those Plex users that won't fix their damn remote streaming settings lol
I currently run Plex/Tdarr/Steam-headless using my old 980ti and the metrics given at the below link line up very well with what I'm seeing on my server. For my price/performance/power efficiency needs and based on the info I got from this link, I'm probably going to go with a 3060 12GB. Good power efficiency, a decent DLSS, raytracing, etc bump for the very little steam gaming I do using steam-headless, and a huge bump to both encoding performance and quality.
Also keep in mind that the new the generation on GPU, the better quality the video encoders are going to output. Newer cards are also going to be way more compatible with certain files like 4:2:2, 10-bit, HDR etc. NVENC will fail on a lot of these files when trying to use older cards, like my 980ti.
https://www.elpamsoft.com/?p=Plex-Hardware-Transcoding
Hope this helps!
-Emma
