The angle isn't the only thing. You really should consider, how close to the subjects do you want to be for your composition. The closer you are, the slower the glass can be and retain some shallow depth of field (example 50mm at F4 at close range will still blur nicely). You don't need F1.2 or F2 on a telephoto to blur. Those will blur of course, but often times, especially with the 85 F1.2L the DOF is so thin that their eyes are in focus but their nose and stuff are not (looks completely silly to me, but to each their own). These long very fast telephoto primes are good when doing full body if you want maximum blur, on a fully body portrait. For busts and head shots, you can get away with F2, F4, etc. Sometimes you need to stop down if you're close to the subject so that both eyes are still in focus.
So don't fret over angle.
Think more about what your, or more importantly your subject's, comfort zone is in terms of how close you are to them when taking their photograph and what composition you want from that distance. That will tell you what focal length to run.