The output signal voltage from a microphone depends on how loud is the audio signal. Its sensitivity is listed on the datasheet when an audio signal level of 1kHz, with a loudness of 1 Pa is present. The datasheet also shows a reduction in sensitivity when the DC voltage is reduced.
Typical manufacturers data sheet. Who can relate to pascals in terms of loudness?
You need a spec on output voltage/noise floor related to dBSPL (Decibels sound pressure level).
~28 being a very quiet room that maybe close to the noise floor of your mike.
~70 an office environment.
~100 very loud noise.
~120 threshold of pain.
The sensitivities of electret mics are nearly the same. Smaller ones like used in a cell phone have a little less sensitivity than one with a normal size.
A voltage gain of 60 instead of a gain of 100 is less than 6dB difference which is not much.