I noticed that many times with tube microphones 
With lower impedance somehow it sound much more pleasant. With Gohm range resistors somehow it sounds always worse to me , typically i would call it these days "modern", less character - in the middle way to China
You could also try another thing at this position (could you? am really courious your opinion), cap between two diaphragms - 3,3pF - 10pF range instead 1nF (according to hand drawn schematic, but i wouldn't be surprised if it's 10nF).
I also never found any noise problem, usual am using 22nF and resistor values starting from 33M. No problem at all.
Great info!
With cathode cap you can adjust low end, but it works little bit different than output cap. In most of circuits on which i worked , it was easier to find "sweet spot" of low end especially with more pleasant low mids.
Let say that output cap is like the gain control pot on microphone preamp, then cathode cap is additional "trim" control pot
