Roadrash, I'll have to try that & see.
Asdaq, I get about 9 hrs out of a 14500 & 24 out of an 18650. You could probably get 3 days out of an 18650.

(this is just using them alone in a mod)
Here's what I got out of using a boosted 14500. The first time I tried it, I was using the loesr 100uf 10v caps(surface mount). I got 45 minutes & it quit. The battery was still @ 3.95v. I put in a fresh battery & got nothing.
Today, I used electrolytic 100uf 50v caps & got almost 4 hours. The battery was in need of a charge this time. I didn't have a meter with me, but I put it in a regular box & nothing. The battery is fine, charged it when I got home & used it.
Ok, that tends to tell me that the V rating of a cap matters here, a lot. I would go with that, but I was using a bigger box today. I got creative with copper foil tape & some foam board & made an adapter, the box is set up for an 18650.
I've got a 9v battery box with an 18500 & a booster in it. These caps are 16v. Sometimes it lasts all day, most times not. When it quits, the battery is far from needing a charge. I'm going to change the caps with a couple of 50v & try the 18500 & the 14500 in it & see what I get. If it works like it should, I'll know it's the caps making a difference & not the size of the box(smaller box, more heat). My eclipse tin has got 35v caps, is just slightly bigger, metal, & it's a workhorse. It quits when the battery needs a charge.
I mentioned heat, but nothing I've tried has gotten hot. Regulated 5v mods sometimes do. Depends on how much you're
vaping.
I will say this about the 14500s, there was a lot of vapor, but the throat hit was not as strong as the 18XXX series batteries. I've got a square camera battery(3.7v 1800mAh) boosted & it's about the same as the 14500 when it comes to vapor/throat hit. It does last a lot longer.
DC, there is a big difference between 4.2v & 5v. The booster board, in my experience, does not heat up like a regulator does. It puts out a solid 5v while the battery is between a little over 3v & fully charged(4.2v), also, it only uses one battery & that's a big plus in my book. I'd much rather have the second battery as a spare.
It'll be a day or 2 before I can get into the 9v box & change the board, but I'll post what I find out.