So, I compiled 64-bit proprietary nvidia driver 

on Salix 15.0 x64 xfce (by downloading and fully compiling kernel from kernel.org, then using

NVIDIA-Linux-x86_64-470.199.02.run file from Nvidia website.

anf compiled ffmpeg 4.4 against ff-nvidia-headers from salix repo.

And fullhd video was going at 65 fps!  Cingg was  at just 30, but I guess this is expected due to all this redownloading via pci-e.

blog where I found info:

 https://garysparks.info/post/can-a-geforce-gt710-nvenc/

so, I hopefully have customized nvidia binary installer to test on live dvd my gpu's nvenc/nvdec !