With 2 monitors, and you open and close C3, does it remember the positioning of everything across the 2 monitors?
I think the minimum you'd want to use with C3 is probably 1440p.
I've used regular full HD, ultra wide, and 4k.
But I find that vertical space is the best aspect, so I prefer 4k as my main dev screen. Being able to see more events vertically + more things in object's property window is fantastic.