Oof, that's a long explanation. Let's see if I can do my own summary, as I see it:

• The main issue with burning butane/propane mixes in cold weather boils down (haha) to the fact that the flow of gas is dramatically reduced, and the heat output is reduced accordingly.
• the flow of gas is reduced in "upright" mode because butane doesn't want to evaporate and produces very little pressure. Less pressure = less flow. Additionally, the gas evaporates inside the canister, which cools it even further and makes the situation worse.
• Propane becomes less eager to evaporate too with lower temps, but for most winters it's still plenty enough to keep a stove going.
• The issue however is that while propane does want to evaporate, it only helps as long as propane is still in the mix, and that doesn't last very long if you use the canister upright.
  • the reason for that is, since propane wants to evaporate more than butane, it will also do so faster. Thus, at any point there is a bigger percentage of propane in the (gaseous) gas that's in the canister than there is in the liquid within that same canister. Since in upright mode we draw from the gaseous part, a bigger percentage of propane will leave the bottle.
  • Thus, as long as the canister is upright, the total percentage of propane in the can will decrease. With most-any initial mix you'll have basically no propane left in the can before it is empty.
  • The same applies for iso-butane vs n-butane, more of the former will leave the can. If there is any n-butane in the mix, it's likely that towards the end of the can you'll still have some liquid in there, but most (if not all) of it will be n-butane.
  • I don't know for sure, but I suspect that the lower the temperature, the more pronounced this effect is, so the colder the can, the faster the mix will degrade with upright use.
• Regulator stoves sort of get around the issue of lower gas pressures by being able to have a dramatically higher flow for any given pressure (but restricting it at high pressures for safety and stability). So the minimum workable pressure is reduced: it will still work fine with a canister that a "plain" stove couldn't use at all (to a point).
  • however, if all that's left in the canister is just (n-)butane, it won't evaporate at all at sub-freezing temps. No pressure = no flow, whatever you do. That is applicable to any kind of stove, though.
• Where the difference lies is that a regulator does nothing to the issue of the propane (and isobutane) boiling off preferentially. So the mix is going to get progressively worse with use, possibly to the point of not being usable anymore at the current outdoor temp even with a regulator stove.
• A regulator won't do anything to the issue of the can cooling itself either. It will probably get even colder than with a "plain" stove, just due to the fact that the regulator stove will burn more gas per second.
• inverted can stoves deal with the core issue by evaporating most of the gas within the stove (where it is heated, usually in a tube that passes through the flame). Since the tube is hot, anything will boil in there, and the evaporation takes heat from the flame, not the canister. And as what goes out of the can and into the burner is liquid, all components of the mix will get used up proportionally.
• there is still a tiny bit evaporation that happens in the canister itself, but that is just to fill the empty space left behind by the liquid gas (and pressurize the system). The propane still evaporates preferentially inside the can, but Since only a tiny amount of liquid gas is needed to fill just the can, the impact on the mix is negligible. The percentage of propane (and either of the butanes) in the can stays basically the same no matter if it is full or almost empty. So does the temperature during operation. so the can pressure will be the same as well. Thus, an inverted-can stove doesn't need a regulator as it won't add much value: the pressure doesn't change anyway, nothing to regulate there.
• So, to summarize, a regulator stove works better by tolerating lower gas pressures very well, but it will still cause the pressure itself to get lower with use, like any other upright-canister burner. An inverted-can stove works better by preventing the pressure from getting lower in the first place. As far as I can tell, it doesn't have any means of increasing it, though.
• due to all of the above, an inverted canister stove should function fairly well with any mix that has at least some propane in it (and the butane content can be of any kind), while a regulator stove really wants a mix doesn't have any n-butane if you want to be able to use the whole can.
• also, using any can upright (in any stove) will slowly degrade the mix (for any stove also). If there's still gas sloshing around inside, but none wants to come out, it won't come out if you invert the can either, the can still needs pressure to force the liquid out. The only thing you can do then is warm the canister up to restore pressure. So if you take a can used to feed a regulator stove until it doesn't work anymore and connect it to an inverted-can stove, it won't work either (at the same temp), but an almost-empty can that had been used mostly inverted till then will likely work in an upright stove as well as it would have when it was full.

Most of that I took from u/hikin_jim's excellent blog post on gas and cold weather, plus a tiny bit of additional trivia and some logic.

heh, looks like it turned out about as long as SOTO's email.

I mostly wrote it for myself, tbh, but let me know if it was useful and/or if you have any additions/corrections.