Imagine you think Laplace is the last word on black holes. That is, you are aware of the radius for which the escape velocity is $c$, but you think gravity is Newtonian. You set your spacecraft on a course meant to be a hyperbola that remains just outside the event horizon of a giant, nonrotating black hole. Tidal forces are not a problem, and your plan is simply to observe conditions near the boundary.
Unfortunately, gravity is not Newtonian, and once you get inside the photon sphere you will need to exert thrust to get back out. (I originally thought the ISCO was the key boundary here, but it's not.) The closer you get to the black hole, the more thrust you will need. My sense is that, even when tidal forces are too small to be a concern, there is a closest distance that any object made of matter can get to the event horizon and later return to infinity without being crushed by the acceleration it would have to undergo to escape the photon sphere.
What I would really like is a number, something like the closest you can get to the event horizon and then escape without any object larger than a meter in height being reduced to degenerate matter. But that is still too vague to answer. So instead, is there a formula for the peak thrust you need to return to infinity as a function of the minimum number of Schwarzschild radii from the center?