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

Google EFI university and look for some of his videos on spintron development. Valve weight is a big deal, even at 6000 rpm. If you can spend a few hundred bucks and save valve weight it’s cheap money spent. Also, if you have your poop in one group you can use Ti retainers and save there too. You can’t make the valve side too light. Weight is a killer.
Yeah, you can be too light. When **** starts breakin from havin holes in it.