Physics curiosity: what is the minimum F/kg of a single bound object?
Something spherical to be sure, and something big to be sure: at given density, mass goes as r^3, while capacitance goes as r.
The interesting part is that, as objects get heavier, eventually they get smaller, as gravity crushes against the compressibility of the material. Degenerate matter goes as r ~ m^(-1/3). Presumably, you'd want to find the densest, heaviest degenerate matter, just before it collapses into the next state (unless that next state is even denser). Well, that describes either a neutron star or a black hole, so I guess that's that.
Incidentally, a black hole possesses charge, so it's still meaningful to speak of its capacitance.
Black holes (non-rotating) have radius ~ mass, so it would seem the F/kg becomes fixed in this limiting case. Heh, neat. So it doesn't matter (at least to a first order) whether it's a microscopic or supermassive one.
Tim