I'm wondering the same thing, what is the runtime on medium?
Well, I just did some tail cap readings, and I would have to say it is hard work trying to compress that foam ring to make contact and hold the probes..
anyway, with an Eneloop, 2000mAh first gen white which had min. rating of 1900 but last tested to be 1958 mAh I got the readings:
firefly: N/A, low: 0.04A, medium: 0.25A, high: 1.9A
so medium based on a 2000mAh battery would give you 8 hours.
Funnily enough, low should actually give you 50 hours and high only 1 hour. Sorry, multimeter just couldn't get low enough for firefly, just a cheapie.
The other strange thing, with an Ultracell 2000 LSD from Aldi, Imedion 2100 LSD, Turnigy 2200 LSD, Varta 2300 LSD, all readings were the same except high, which hovered around 1.5A and 1.6A. Voltage sag does seem to play a part. Might have to do some ceiling bounce readings.