Quoting: Xpandercompton is all good but makes the windows move slower and takes a bit perf hit.
also recording will be pain with compton. there will be screen tearing on the video

Try compton's xr-glx-hybrid backend. Might require a recent git snapshot of compton, I'm not sure. Makes the desktop very snappy. That's what I do on my work computer. I'm happily using the glx backend on my gaming box though, as window move performance is hardly a priority. Compton has no effect on fullscreen gaming or video as far as I can see. I haven't tried recording on either, but that's where tweaking compton's vsync method might help.

So, I have basically solved it using two scripts.

Thanks to this tweet: https://twitter.com/HeavyHDx/status/730818366148071424

Essentially I now have a shortcut assigned for two scripts, one to set ForceFullCompositionPipeline on at 4K resolution and one to set ForceFullCompositionPipeline on at 1080p resolution.

It seems when games change the monitor resolution instead of stretching a fullscreen window (hello Stellaris), the ForceFullCompositionPipeline option is actually reset.

Why am I doing some games at 1080p? Performance, text being too small etc.

So I am just doing this:
nvidia-settings --assign CurrentMetaMode="DP-4:3840x2160_60 +0+0 { ForceFullCompositionPipeline = On }, DVI-I-1:1920x1080_60 +3840+0 { ForceFullCompositionPipeline = On }"

And this:
nvidia-settings --assign CurrentMetaMode="DP-4:1920x1080_60 +0+0 { ForceFullCompositionPipeline = On }, DVI-I-1:1920x1080_60 +1920+0 { ForceFullCompositionPipeline = On }"