Pretty cool tests!

One thing that struck me was that even though the tests were conducted in temperatures above freezing (just barely, but above), the cold was affecting the tests. The warm canister beat the cold canister by about a minute, and this using an isobutane/propane mix. Isobutane vaporizes at 11F (-12C) and propane at -44F (-42C). The air temperature was some twenty degrees Fahrenheit (about 10 Celsius degrees) higher than the closest vaporization point, but the tests were affected.

I think you may see where I get my recommendation of 20F as about as low as you want to go with an isobutane/propane mix (except in liquid feed mode) even though isobutane will continue to vaporize for another nine degrees Fahrenheit below my recommendation.

It would be interesting to see your tests repeated with nearly empty canisters -- after the majority of the propane is gone and most of the mix will be isobutane only.

HJ