Hi KowShak - I hope you are enjoying an open and friendly technical merits discussion about LEDs and flashlight use as much as I am. :twothumbs
I have become a bit spoiled by Lumileds and their really excellent binning specs, esp. when it comes to Vf. If you are using a real constant current driver, Vf largely does not matter from a "making it run" perspective. I hardly ever use "real" drivers, so Vf is a big deal for me.
The downside of my approach, is that it limits which LEDs I am able to really use, as knowledge about the Vf (and some games I play to lower it even more) are not really available to me with Cree and SS parts. I don't make so many flashlights that it really matters, so for my use and limitations - restricting my LED use to LL and highly binned LEDs is not a big deal. (I am too lazy to repeat all of my prior work for optics, heat sinking, etc.)
A useful example is the much maligned Lux V. If you look at the "typical specs", you would conclude that this part is more or less of limited value - 5 watts to make 120 Lumens is non - competitive. OTOH, reality is quite different, as it is possible to obtain XWOS binned Lux Vs. In other words, a phenominal color bin, about 200 Lumens (rated) at 700 ma, with a REAL Vf around 7.5 V @ 700ma. This is one heck of a light thrower and working with them on a bench is nearly blinding.
The R/O Lux III is similar - you can get some amazingly bright, low Vf parts that are dramatically different than the tyical part. Look for Photon Fanatic in CPF marketplace and search around a little.
I will admit that I have not personally tested the absolute latest LEDs from Cree and SS, but my prior testing of their parts (and LL parts) was that very little more light was gained driving them above 75% of rating - especially if you have limited battery power like a 2 x AA supply. Even with good heat sinking, efficiency falls fast with added power. You might see the "super bright start- up event" for 10 - 15 seconds, but after a couple of minutes - forget it.
The lumens per watt numbers from all suppliers need to be taken with a grain of salt IMHO. Those numbers usually come from an "insta test", sometimes at very low currents.
I should dig out a light that photon fanatic made for me - with a Lux III r/o and find an SF L4 to compare it to. This would probably work, but I am not sure that I know anyone with off the shelf lights around here.
In any event, I think you will find that a well binned Lux III R/O will be about 60% of the Vf of a "typical" Cree white at 1000 ma.