Does anyone have a tried and tested favorite 3D Settings for their 30 series GPU? I watched a few YouTube videos and everyone seems to do their own thing or have their own opinion.

Hoggle
A lot of it would depend on what games you like as some changes can be major in some games and minor in others and what type of system you are running as the monitor for one person might make some settings look better than others.

This ^^^^ it really depends upon what monitor....what games and if simply gaming or benchmarking....
 
With gaming, I found I had to enable Max Performance playing Fallout 4 in order to get the GPU to climb out of power saver clocks....older title.

The settings that I generally use for pretty much all my games (with a 3080 Ti) are:
 
Ambient Occlusion: Quality (this is just personal preference; not everyone will necessarily want that)
Low Latency Mode: Ultra (I don't really know of any downsides to using this setting)
Power Management Mode: Prefer Maximum Performance (unless you're concerned about your power bill, I don't really know of downsides to this setting either)
Shader Cache Size: Unlimited (I don't see any reason why a rig with your specs wouldn't use this)
I leave antialiasing set to be application controlled and deal with that in-game.
 
And since it looks like your monitor has HDR, I'd recommend a couple of settings regarding that:
      Under "change resolution" instead of using the default color settings, click "Use Nvidia color settings" and make sure dolor depth is set to highest, output color depth is 10 bit, color format is RGB, and dynamic range is set to full.  Your settings might appear a little different than mine since there are umpteen different HDR standards out there, but basically make sure that everything is set to the best quality.  Be aware that some games might not play well with HDR though, so if things look washed out or weird (or crash like I think Deathloop still does in HDR, although I've never tried that game so don't know firsthand), you can turn these back to default settings.
      Similarly, under "adjust video color settings" click Nvidia settings and set the dynamic range to full.  I also turn up digital vibrance a bit under "adjust desktop color settings", but that's just a personal preference for me since I like my colors to pop (using an LG CX48 OLED monitor).
 
Other settings are more game dependent or a matter of personal preference.
 
Just my two cents.
 

I've never had any success or noticeable improvement on 30 series cards with fiddling with the Nvidia settings, I let them ride and change things in game to optimize to my liking. 

It only causes me grief...do what you want.