Hi
I am very happy for you that the 3070 works like a charm.
To me the best way to obtain high quality is to oversample original to x4 and build what is called a “master”. If you have enough RAM, output it to 8b 4:2:2 or 4:4:4 Then you start to work on it, removing noise, sharpening it aso… The final process should be downsamling.
This is what is done in the movie industry and in video games.
But … be carefull downsampling is the harmfull process, because it creates some artifacts or aliasing.
You should read this topic to perform it followinf your need and also what TVAI was able to output.
The last link is kind, because it live simulates rendering by clicking.
My favor goes to Calmut-ROM algorithm, an excellent comproise with sharpness and smoothing edges.
Best overall is Lanczos3 optimised with spatial sync (w/ Fourier’s transformations)
You can find it in many free encoder.
If you choose TVAI, Kyle said Theai was good for this treatment.
Again my favor goes to a CPU treatment because of floating point accuray. It is essential for downscaling.
Such downscaling should be run then on the most overkill CPU you have for best quality.
For compromise use TVAI or DVR Studio.
My personal process is
- Upscale x4 with VSDC or TVAI depending on source.
- Clean, sharpen, denoise, aso TVAI as an evidence saved as FFV1 of High profile HEVC
- Downsample with SVT-AV1 because the only one to use 16 cores for encoding (2990WX)
1 week for 2 hour of 4K video 
No compromise, it’s perfect or it’s not 
