I sometimes run a 91B in a VME head and a 16650 LiIon. In round #s, the 16650 is good for about 2000 mAh, and I get 45 minutes of very solid, slightly declining output, and then another 10 mins with sharply dropping output.
With a 16340 at say 900 mAh, I suspect you'll get about 15-20...