Jerry, you might want to ignore the details in my explanation, after I got schooled on it. :-)
An (important) correction: I checked my stove log, and found that the coldest I'd operated the Coleman Exponent stove with Powermax fuel UNDER THE CONDITIONS I STATED (fuel actually at ambient air temperature) was -25F, not -30F. I've used the stove at -30F and lower, but on those trips I always did something to keep the canister warmer than ambient.
So, I've been trying to reconcile my experience with the operational limit of my Coleman Exponent stove being -25F, with Stuart's comment "you can expect the stove to work with an inverted canister down to 0F." However, after looking at the charts, it seems both of our statements can be correct (after mine was corrected ;-). The left chart of Fig. 4, typical canister mix at sea level limit is -23C, +5 degrees to get some working pressure, so -18C = 0F. The right chart, Powermax fuel (30% propane, 70% iso) at 10K altitude (where I use the stove) limit is -36C, + 5, so -31C = -24F. Assuming I haven't screwed up again, that explains why my stove operated (poorly) at -25F.
Thanks, Stuart and Roger, for reminding me about your excellent article. I forgot just how much difference mix and altitude make; I'll try to remember that when I'm outside Wyoming. Also, thanks for clarifying the mixed-gas boiling science.
To the original question, perhaps the most relevant point is that, while all canister stoves stop operating at some low temperature if you don't do anything to keep the fuel warm, you can run these stoves regardless of the air temp if you simply keep the canister at, say, +32F. As mentioned in this thread (and in the article), that can be done with a pan of liquid water. The bottom cover for my original JetBoil is has a diameter just slightly larger than a small fuel canister, so I set the assembled stove in the cover and fill it with water. After a while a skim of ice forms on the water, but it runs just fine. For my Coleman stove, I usually work-pack the canister in snow to keep it 'warm' and prevent it from chilling in the overnight air.