Thanks guys for explanations.
I've putted the HO-9 in my 9AX.
It's true I see a difference in brightness when use with 2x 18500 compared with 2x RCR123. Much bright and whiter too.
The standard 200 lumens W-E LA is installed in Surefire M2 with 2x RCR123's.
Safer for the cells, because drawing less current than the HO-9.
Beam is yellower, but hotspot is very big ! I like it.
With HO-9, I had done a runtime test, 20 minutes before cells need charge (3,08V after 20 minutes).
How about the runtime with W-E 200 lumens + 2RCR123's ?
Similar to HO-9 I suppose.
Now I'm waiting fresh news about the new Cree modules from Wolf-Eyes, to find its place in my D2AX !
I hope really the regulation will be flat when use with single 18650 cell.