As mentioned, you can only rescale in old nvenc. As I have a dual PC rig, I stream with x264 and record with nvenc (new). Canvas at 1440p, recording at 1440p and streaming rescaled to 1080p.
Downside of rescale: it has no scale filtering (bicubic, lanczos etc) like downscale does. You'll get a slightly blurrier output.
I'd love to have scale filters for rescale.