Hopefully Jon will chime in, but this is what he told me about the MSH-1O's:
Yes, the electronics are a little different
(than the 1A's), so I could use the same
bits for the 1O and 1C. Sensitivity is higher, SPL handling is higher
by 6dB, and the 1C is much higher, 124dB at 1kHz, but that is where the
mic is most sensitive, so for bass frequencies it could easily be 10dB
more. The 1C is tailored response though, so
I am not sure how desirable it would be for some applications.
Looks like I need to get the 1O's now...