@kerrybh Thanks for taking the time to reply.
That's an excellent point. Tonal preferences aside, if "the best" cartridge represents 5, 10 or 15% of the total sound of a system, dropping a step or two down in the family would not drop that down to zero.
I suppose another way I could have phrased my initial question was "what % of performance is the model 1 or 2 down from the top?"
That doesn't quite get to the matter either.
I realize much of what we do is chasing the marginal gain, and sometimes the difference between "something is verrrrry slightly off" and "everything is perfect" can sound small when expressed in percentage terms (eg 99% vs 100%) but perceptually is more noticeable.
I also wonder if the rest of the system is highly revealing, does any weakness of a slightly lower performing cartridge get more brutally revealed. Or, is it that the cartridge 2 rungs down the ladder will sound good on an excellent system and good on a lesser system, but the lesser system would not be capable of presenting the top cartridge to it's fullest potential?
These are questions with no correct answers. My post is an attempt to foster discussion. I realize this is an imperfect process.
Thanks for everyone's thoughts.

