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

It depends. I use a mp long 2.08 intake on my w2,s. I have .705 lift at the valve. The stems are 3/8. over 650 pounds of open spring pressure. I do have titanium retainers and 10 deg single locks.
How much would I gain going to a smaller stem versus the reliability. Not to mention the cost. Not worth it to me.
What’s that valve length again?