Entirely seriously and not trying to be rude:

Learn how to write better supports tickets / help requests.

Your title implies you need help with an initial efficient set up, but then you go on to describe that what you actually want is help figuring out why moonlight/sunshine/steamlink streaming is quite slow on your system.

Just be that specific in the title.

There are tons of different ways a system can be efiicient, things it can be optimized for, both in hardware and software terms. People see a title like you have and generally think its someone asking a pretty broad question, a different question than what you seem to actually want the answer too.

Now to attempt to answer that question:

Well, you say that RDR2 and CP77 run decently well locally as compared to when it was a Windows machine, so it seems the pc itself is doing ok... but, we have problems when trying to stream it to other devices.

What are those other devices? What are their speces/configuration?

What is the network card on this resurrected pc? Does it have drivers that work with your streaming software?

What about your wifi router, what are its specs, model number, settings config?

With streaming, we are now talking about at least 2 devices that all have to meet min specs and be configured correctly, at least 3 if you're doing this wirelessly.

Also... were you doing local wired or wireless streaming from/to this device back when it ran Windows, for a point of perfromance comparison, or are you just trying this for the first time when it is now a linux machine?

Streaming like this, the streaming itself is actually often quite a demanding and intensive process, its fairly likely using that rig that just barely, roughly meets CP77 min specs... well, throw streaming on top of that and now that machine is basically below min specs.

This is why say Twitch streamers who play very graphically intensive games at high to ultra settings tend to have absolutely monstrous rigs, or just throw in a dedicated capture card or device of some kind... realtime screen recording and transmitting is an intensive process... even a 2 to 3 thousand dollar modern setup is gonna lose maybe 5% ish off its avg FPS just doing local screen capture, muchless also realtime transmitting it.

IRT Steam Link for linux, it is relatively new and is probably still working through an initial 'growing pains' type stage of proper linux support on basically all conceivable hardware, its not even 2 months into its official, initial linux release.

https://itsfoss.gitlab.io/post/valve-finally-makes-steam-link-available-for-linux-gamers-to-stream-games/

More info:

https://linuxvox.com/blog/steam-link-linux/

https://www.linuxmadesimple.info/2024/06/how-to-install-steam-link-on-ubuntu-2404.html?m=1

https://help.steampowered.com/en/wizard/HelpWithGame/?appid=353380

Moonlight/Sunshine:

https://github.com/moonlight-stream/moonlight-docs/wiki/Setup-Guide

Two of my family members are still rocking machines of this vintage. Get a Vishera-based (8300 series) FX CPU if you can find it cheap, so you at least have x86-64-v2 instruction set. It helps. You probably have (Realtek?) gigabit networking onboard, but an Intel gigabit card will improve networking performance.

When streaming, you're running the game and encoding video at the same time. This will make the PC double as a space heater, which might be OK if you're in the northern hemisphere and approaching winter! 😉

Heh, TFW someone describes "resurrecting" a "low-spec" machine, and others talk about how old and out of date it is, and it's roughly equivalent to your main gaming PC.

To help narrow it down I'd try streaming a low-end game that runs very well locally and doesn't tax the system. If this doesn't stream well either that would suggest that it's something specific to the streaming setup, perhaps a networking issue.

Maybe codec? maybe instead of hardware encoding h264 it's software encoding av1

By "stream it", do you mean sending the video somewhere for other people to watch, or do you mean running the game on this computer while playing it from another one (aka remote play)?

The slowdown you describe could be explained by a slow video encoder. Can you configure Steam Link / Sunshine / Moonlight / whatever to use the GPU hardware for encoding?

16 GB RAM is sufficient, though with an FX 8120, Kubuntu might be a bit steep... if you want an Ubuntu, I would strongly suggest Lubuntu for the lightweightness, unless you absolutely need Wayland.

As for the Moonlight problem, make sure you have the nvidia drivers installed, and you also use nvenc to encode in h264 or h265.

It might be the old motherboard and chipset. If they don't have good speed they won't be able to keep up with the bitrate or bandwidth necessary for streaming. Old chipsets weren't made for it since it wasn't a thing years ago. Just to name one component, newer PCI express busses are sometimes 10 to 100 times faster than older formats (like PCI-X). For example, PCIe 8 doubles the speed of PCIe 7 that is barely 3 years old, imagine compared to even older versions. This is necessary to keep up with internet modems and the typical speeds and ping times required for game streaming with minimum lag.