Not entirely sure I agree with your gain/ noise comments? ......
If for example I take note of? a preamp noise floor reading, and then record a signal at - say - a level of say -40dB, and then remove the signal source, then obviously the noise floor reading will still register the same.
If I increase the gain of the signal source by 10dB to -30dB, record again, and then remove the signal source, the noise floor will, once again, remain the same.
IF however I return the signal source level to -40dB and then increase the gain of the preamp by 10 dB, I can once again record a signal level of -30dB.
If however I then remove the signal source and observe the increase in the noise floor, I notice that although the gain has been increased by 10dB, the noise floor will only have risen by some 6dB on the particular pre-amp I'm using (In this case a Sound Devices USB-pre).
The actual amount of noise increase will vary between different preamps of course, but with most high quality mic preamps, you would expect the gain to increase by more than the noise level!
If however you are increasing the gain of an early noise source, then that noise will obviously be increased by the level of the gain applied by following pre-amp.??
So there can be advantges in increasing gain in the highest quality part of the signal path, which may not always be the mic itself.
Where - as you mention- you're running short of gain anyway, you don't really have choice but to add gain early on....?
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