The D3AA should be included, the driver of that light is ridiculously efficient. On moonlight modes it struggles a bit, but on any mode higher than that it is very efficient. Have hank or jlhawaii put some low CRI LEDs in there and it will be even better. 3 SFT40 5000K for example should make for a very efficient, slightly throwy light.
It really depends on the driver. A very efficient boost driver will remain very efficient even at lower loads. Actually, the eff curve usually peaks somewhere around medium loads. This is essentially the same driver tech (different PCB, similar schematic from the same designer) as used in the D3AA, with some nice efficiency measurements: thefreeman’s HDR Anduril 2 high efficiency drivers - update : FWxA boost driver - #319 by thefreeman. 200lm out of somewhat efficient low CRI LEDs should be ~0.5A.
EDIT: I forgot this is a 9V boost… 0.5A 9V would be way higher than 200lm, 0.5A at 3V should be in that range.