Exactly as Flash said, its subjective.
I tried a couple an found what FG said is correct for me too, 20-30 ohm.
Still lots of light to navigate with and not disturb others indoors, now i am running the Li-Ions in my 2 KL1's(E1L,E2L) and have since removed the resistor to get a clicky back and run them at full juice.
I meantioned in one of my first posts that i use Rubber automotive vaccum caps on the ends of my lights, the lens end an switch ends on the ones where feasible, i have since found kitchen table chair leg caps, they go on the bottom of the legs. Anyways they come in standard fractional sizing and a 1 inch with a 1/4 hole in the middle i put in makes a nice nav light now, and fits the 1 inch bezel perfectly. Did i mention i like my stuff clean, also a pop bottle cap liner inserted makes a poor mans diffuser.
Buy a box of 10 ohms, and touch from the barrel to battery bottom of the last battery and bypass switch, if not dim enough add another in line. Then when you find a good value, get the closest single an add it in.(To save room)
Peace
IF