So about the Arc a380...

[Host-in-the-Shell]

I did test it without resizable bar, as I ran it like that for a few days at first. I can say the quality as well as performance certainly improved with it on. A noticeable difference was with tone mapping which looked a little drab and washed out when I ran the card out of the box. There was also some artifacting or white dots but the BIOS update could have fixed that instead of the other stuff. With it on I see about 10-15% usage on my cpu (ryzen 3 3100) when somebody transcodes remotely and it can handle the 4 people that connect to it on my server without issue. Without it there is far more cpu usage but I don't remember the specific amount. Unfortunately I cannot bring down my server at the moment because it would be disruptive for several of my self hosted services and to the people who use my media server. If you don't have to service several users, I think the A380 can transcode just fine without resizable bar and the visual hit is not that bad, at least IMO.

EDIT: There's also the posibility that the BIOS updates helped with performance and stability in general; keep in mind I haven't retested the card after updating the BIOS.

As for ASPM, there is more information you can read about here. That only details how to get it working on Windows, however, and since I'm using Linux, I had to configure it through the BIOS settings.

I've attached a screenshot of my current playback settings so I don't have to go over each one in case you'd want to know.

EDIT2: I forgot to mention that in terms of power consumption and energy efficiency, enabling resizable bar didn't really made much difference in terms of increased consumption. Before I was running a really underpowered laptop for my media server that I regulated and optimized using TLP, so I always expected to pay a higher electrical bill with the new server, but to my amazement my bill increased by only 1-2 US dollars at the end of the month. I'd call that a win.