Gentlemen,
Allow me to give my 2 bits worth. I am still tickled that I found this forum and feel it is great.
Remlap,
My views on your questions are as follows:
1) You probably shouldn't care what the natural frequency of the mount is. I am assuming you are using the anti-vibration mounts as mounts for something else, probably much bigger and heavier. It is important to keep in mind that you are after the overall SYSTEM response, and not that of one individual component (probably). The characteristics of your dampers will contribute (hopefully a significant amount, as that is what you are using them for) to the overall system dynamics.
2) My view is to say no, you might get in trouble assuming similar mechanical characteristics (and resulting system response) on two different mounts with near identical F vs D plots. The reason is that the stiffness is only one values that you need and damping is the other. To me it doesn't seem impossible to have two material/geometry configurations that match one and not the other. However, providing your mounts are "similar", your assumption seems like a good place to start to me. If your tests are long and expensive, then maybe you can run the test with say Mount A, and record the response. If your part "passes", then just jig it up with the second mount, and compare overall response. If it is similar, then maybe you can not test the second mount out to 6 weeks, 10 million cycles, etc and have some confidence in it?
Side note: (You may need to be aware that materials can give different F v K plots depending on how they were generated: statically or dynamically)
Electric Pete,
Your logic is good, but as I think was mentioned above, you are not necessarily better off to just pic the one with the higher energy loss. (sorry if I sound like a lawyer). You can view hysteresis as energy loss. Again, the overall system response is what you are after, which will be sensitive to the mount characteristics. The damping of the mount shifts the natural frequencies around. So, allthough the higher damped one may absorb more energy, that benefit may be lost if you are moving the system closer to resonance.
Hope I helped, and didnt mislead or say something inaccurate. Good luck.