Further to my previous replies I now have an RTX3060ti and it causes me problems whereas my 1660s did not.
From some wikipedia entries I believe the 3060ti and 3070 share the same 'chip'
I notice everything is slightly blurry / fuzzy, there appears to be by default no sharpening whereas the 1660 everything by default is much sharper even on default settings (same driver versions, resolution, display, cable etc all the same)
I'm playing with settings the RGB to limited, this massively dulls the color output even on my TN screen (not tried it on an IPS) and I've also attempted to disable dithering via a registry change.
Another thing is setting the Nvidia control panel to enable image sharpening, this is off by default and turning it on sets it to 50 (%?) and this makes the image look more how the 1660 outputs.
Still have a migraine though, eyes not so much pain but its definately giving me significant head pressure pain which my dr said was migraine.
I shall continue to test.