Does GR put a theoretical lower limit on the radius of a black hole event horizon? Within GR theory, without going to the extreme r/0 as a radius, (but approaching that as an asymptotic case), is there any theoretical limit as to how small the event horizon of a rotating and/or charged black hole can be? 
I appreciate that the Hawking radiation hypothesis postulates that micro black holes, especially primordial ones, should be hard to find, due to evaporation although, as far as I know, this is still a speculative idea, with unfortunately no definitive data to confirm or falsify it. 
I am also aware of the possible basis of Planck lenght effects, but again, as far as I know, these are speculative ideas, without observational proof.
To sum up, I want to ask this question regarding GR within the observational effects we have already confirmed.
EDIT apart from CuriousOne's comment, which is true of course, I need 1 assumption for this particular question! END EDIT
 A: General Relativity is a purely geometrical theory of gravitation.  Quantum effects have no place within GR, and more generally there is no scale to GR itself.
For example, if you look at the Schwarzschild solution, you can set the mass $M$ to be whatever you want.  But if you change $M$, you can also scale the time coordinate $t$ and the radial coordinate $r$ so that this has no effect.  To be specific, just define new quantities
\begin{align}
  M' &= 2M, \\
  r' &= 2r, \\
  t' &= 2t.
\end{align}
This also gives you a Schwarzschild solution.  Plug in any (nonzero) number instead of $2$, and you've got another solution.  This is why we can't derive the length of a second from GR (we arbitrarily choose it related to a frequency found in quantum effects).  Instead, you can only derive scale-invariant ratios.
Of course, GR is only an approximation to what scientists believe is the correct theory of the universe.  And there are regions of parameter space where that approximation is believed to be wrong.  One of these is at the very small scales where quantum effects are strong, which is why the Planck length might come into it.
So within GR itself, there are no limits.  But GR isn't the end of the story, and we don't know the end of the story yet.
