How can I optimize my AMD Ryzen 9 7900XTX or 7950X3D for lower power consumption and heat generation while maintaining high performance during streaming and gaming?

You’ll have to undervolt both, your CPU and GPU. If you’re not familiarized with the term here’s a general idea of how it works: when do do an overclock you’re basically increasing the power consumption of either your CPU or GPU by raising the clock speeds and voltage in order to gain performance; on an undervolt you’re doing the opposite, you decrease the power consumption but! contrary to what you may think you don’t necessarily lose perfomance because you can just decrease the wattage without touching the clock speeds, that means that you can retain the “same” performance but with a more efficient power consumption. In reality you do lose some performance but not that much so it’s a good trade off, also the best part of undervolting is that there are no risk to damage your hardware unlike the overclock in which you can melt your components XD, worst case scenario while undervolting is to get a blue screen, no problem, just restart your computer and you’re good to go since you do it via software, you’ll need ryzen master for the CPU and MSI afterburner for the GPU, I think that you can also use the adrenaline software but I’m not certain about that since I’ve an Nvidia GPU.

I undervolted my laptop and got pretty good results (I did it mostly for thermals) but I’m no expert by any means, so there’re lot of resources on the internet on how to undervolt, a quick search on youtube and you’ll be on the right way.

In regards of your other question, I only know two programs: Streamlabs or OBS, none is better so depends on your preference, from my short experience with both softwares: streamlabs is more user friendly and eazy to navigate if you’re new, but migh feel short in terms of advanced features; OBS it’s more robust but to my perception is more for advanced users who already know how to dial settings here and there, so the learning curve might be a little more rough if you’re new, also OBS consume more resources from your computer. So again, youtube might be your best friend to clear your head or just download and try both, I mean, at the end of the day both get the job done. So I hope this was helpful and good luck with your streamings.