At what point would you step up to ferrea hollow stem valves

Bewy said

Conical springs come in double springs, not sure about triple. Less weight, lighter retainer. Never heard of beehive triples....

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As I said, they were prototypes, the member even posted a pic(s).....hoping they chime in....I know IQ52 was retiring from this stuff....not sure which forum/thread it's buried in....