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

I don’t know how my reply above got messed up, but here it is again.
https://libertysgears.com/services/face-platepro-shift-gear-modifications/
Face Plate/Pro Shift Gear Modifications | Liberty's Gears

The same/similar question at a Mustang board
How does a faceplated trans help you shift any faster...