I've noticed that the AW 17500s are very strong performers for their size, they clock in over 1AH into heavy loads, and over 1.1AH into light loads, very conservatively rated. I haven't seen discharge graphs of AWs 18500, but most 18500s I've seen in Toms li-ion shootout only seem to be around 1200-1300mAH.. if that holds true for AWs, then 4 17500s would have more watt-hours than 3 18500s. Hard to say though, if AWs 18500s hold up to their label capacity, then either configuration would have about the same watt-hour capacity.
For many applications, 3 18500s would be great, if you were willing to push the envelope on li-ion limitations a bit, use it short bursts and charge often, they could be used to drive an 1185 in a 2D host...(this would probably require moving the switch forward, or machining out the tailcap, or both, etc etc)
I think the 4x17500 adapter would find it's "sweet" spot for users who are trying to use something like a maxflex driver to push a bunch of LEDs in series, having higher input voltage improves efficiency of the driver and reduces heat problems at the driver. Would be a good setup for driving 6 LEDs in series. With the output set to 1A the current from the cells would be about 1.7A. ~30-40 minutes runtime and ~1500 emitter lumens.
Another idea- a tri-P7 setup in a 2D (not even sure if parts are available for such a project), buck regulated from 4 li-ion cells would be ideal to keep em in regulation- Could drive at 2.8A with a runtime around 25 minutes. That's 2000+ emitter lumens from a 2D host, not bad.
That's just a few things on my mind that the adapter could be used for, there are certainly other setups in a 2D mag that are competitive, the 4x17500 option really won't open up any doors to a higher level of performance in a 2D host, but may make a few projects more feasible. Sometimes it's fun to just have something a little different
If I see a handful of people interested in this design, I'll give it a whirl, I have to focus on finishing 2x18650 and then 3xAA adapters as planned. This project would be the next on the list if it's worth doing, hehe.
Eric