I think very large stones look best in more shapes less faceted, like an emerald or asscher.
We have a good family friend who is very wealthy. Her original e-ring is now worn on her left hand and appears to easily be a 12 carat asscher stone, she moved it to left hand when her hubby gave her a giant emerald on their 30th anniversary, it also looks to be easily 12-15 carats. She wears them well, they're very understated settings and she's considerably taller than me. But they wouldn't look as good in RBs in my personal opinion.
My RB is just over 4 carats and I cannot imagine being able to wear anything larger on the daily, I do have a small ring size, but still! lol