There is perfect logical sense to this and has nothing to do with a gut feeling or reaction comparing 2 products that are very similar. In this case, you are comparing 2 very different products. One is designed to sustain higher voltage into higher loads for a shorter period of time, the other designed to last a long time regardless of voltage sag. (well, I would argue that anything with the ultrafire name is designed to be sold at a really low price regardless of performance but that's a different argument in play all together).
The IMR cell keeps you above a threshold of performance that you desire for a longer period of time than the LiCo cell. This is not surprising. Generally speaking, IMR cells hold a flatter discharge in many comparisons, even though that don't actually have as much capacity. The ultrafire LiCo cells may very well have more available capacity, but you are probably dropping below the voltage you desire for good vaping earlier on the ultrafire cells.
I use little IMR14500s for my PV. I can get a whole day out of one just fine, but when I'm drinking beers in the evening, often here on front of my computer, my craving for large hits and vapor density increases. I may swap the cell out several times through the evening so that I can get all my hits from the top of the charge of these cells. Nice thing about having a Pila IBC, I can feel comfortable leaving a cell or 2 on the charger all the time with no worry about overcharge or danger.
Eric
Yes, I know, anecdotal, schmanicdotal, but would this explain why a AW IMR 18650 1600 mah will get me through a whole day of LR510 vaping when the Ultrafire 18650 seems to poop out, despite being almost twice the mah?
