It was a rough frequency sweep, by manually tweeking the signal generator.  The measurement was only between the microphone output & preamp output.  The instruments were tested to be flat.  As expected, the higher the gain, the lower the cutoff frequency.  The higher R ratio just makes it less flat.  The 4Mhz GBW of the LF353 did what GBW's do.  

 Surprising to see so much loss in the low frequencies.  It was good to see the peak gain achieving the full R ratio.

A younger lion would have had a digital pot clearly showing the point where the gain crossed 100x, with an option to go to 400x.  An old lion just limits it to 100x.

In terms of the microphone's JFET amplifier, its voltage gain was consistently 2 across the frequency range.  

This page

http://sound.whsites.net/project66.htm

had some nuggets about noise.  Manely, fixed regulators are noisier than adjustable regulators.  A resistor alone generates 260nV of noise.  There are formulas for converting the op-amp's stated noise density to a SNR.