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

Somebody would have to explain to me how valve weight affects spring pressure. It's the lobe lift that dictates spring pressure. At least that's how I see it......maybe I'm misunderstooken.
Controlling the valve mass is the spring's ONLY job, the lobes are effectively trying to "throw" the valve into space. The higher the velocity(& remember energy is a square law- 2x speed=4x energy) and the higher the spring load & the frequency tuning has to be. Velocity can be different to the extreme for the same lift so, no........less valve mass means one can use a more aggressive cam on the same springs, or use less spring load on the same cam, with a good beehive offering the best of the latter....