I can see that you already concluded that Diamond dome has to be superior to Beryllium dome. Steve Mowry says in the article "The Whole Truth About Beryllium Diaphragms: -
"For a given geometry the first bending (break-up) frequency is proportional to the material Speed Of Sound, where the speed of sound within a material is defined as the square root of the YoungÂ’s Modulus divided by the Mass Density, (m/s); the higher the better. However, the Mass of the diaphragm must also be considered. Then the ratio of the Speed Of Sound to the Mass Density can be used as the materialsÂ’ acoustic figure of merit, (m4/kg/s); the higher the better."
After that he shows values of "Acoustic Figure of Merit" for different material (higher the better)in m4/kg/s
Berillum - 6.97
Diamond - 4.92
Aluminum - 1.86
Titanium - 1.13
Steel - 0.63
"For a given geometry the first bending (break-up) frequency is proportional to the material Speed Of Sound, where the speed of sound within a material is defined as the square root of the YoungÂ’s Modulus divided by the Mass Density, (m/s); the higher the better. However, the Mass of the diaphragm must also be considered. Then the ratio of the Speed Of Sound to the Mass Density can be used as the materialsÂ’ acoustic figure of merit, (m4/kg/s); the higher the better."
After that he shows values of "Acoustic Figure of Merit" for different material (higher the better)in m4/kg/s
Berillum - 6.97
Diamond - 4.92
Aluminum - 1.86
Titanium - 1.13
Steel - 0.63