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

What’s that valve length again?
I don't recall the actual length of my valves, but they were the long valves that mp sold to get a 2.00 installed height. You need that height to get enough retainer to guide clear because of the cam lift,
You also will have valve springs that will live longer because they taller. But this all makes the total assembly heavier as well.