This feature is called nvenc and is for streaming your output to a website as gamers do with their gameplay and/or various webcam services. It can also be used with ffmpeg to re-encode video at a much faster rate than all but the most extreme systems. I have about the oldest nvidia card that supports nvenc and it is rated at 8x real time 1080. I can get 2.5x real time at 1080 with very good quality. The newer cards are 2-4-8-16x as fast as my card and can do 4k video encoding faster than real time.
It sounds like you aren't doing that. If you were doing that the nvidia cards with their driver are useful and the encoding on the AMD cards is currently I believe rated as almost useless because of poor quality. I tried that with their vega(APU with/ryzen 4500U), and to get the quality decent the bit rates were many times higher than the nvidia card encoded video making it useless all around. Maybe whatever is after vega does better.
What kind of motherboard/system do you have and does it support more than PCI2.1?
Unless you are doing gaming and/or some other intensive video I am not sure how much of a video card you need. I recently converted from multi-monitor to just a single giant 4k monitor and effectively have about the same area as 4 22" 1920x1080 monitors.
If you are using the rpmfusion delivered Nvidia driver, then about the only issue I have had is sometimes you upgrade the kernel before the nvidia driver has been rebuild and when that happens it does not work.