I'd take the black belt a million times over. That's a rare and magnificent treasure, where skill easily trumps strength. It is also extremely difficult to acquire.
It's really hard to get a black belt, it took me 10 years of consistent training in the art and a year after getting it I still don't feel like I'm good enough. That's okay, because it keeps me on my toes: when I feel like I don't want to train, whether it's jiu-jitsu, boxing, cardio or weightlifting, I'm reminded that I have a black belt and I need to "honor" it.
But feelings are feelings, I got a PhD in three years, close a #3 CoC in 6-9 months after getting them, and I got a black belt in 10 years. In terms of "joy of accomplishment," I would put 1) black belt, 2) CoC #3, 3) PhD.
I'd take the black belt a million times over. That's a rare and magnificent treasure, where skill easily trumps strength. It is also extremely difficult to acquire.