Oli, frankly, I believe my nearly debilitating test anxiety did me in. I don't think it was a lack of preparation. I just can't stay calm and focused when I take exams.
I would recommend going to grad school for physics rather than astronomy for all the reasons you listed.
From my experience, the physics Ph.D's have an easier time finding jobs that the Astro Ph.D's.
I found out today that I failed my written comprehensive exams. I'm devastated, ashamed, and embarrassed. I don't even want to show up on campus tomorrow, let alone see my research advisor or anyone on the comps committee.
Our Ph.D program allows two attempts, so I can take the exam again in...