I'd like to dispel a myth that's out there: The myth of "fractioning."
Fractioning suggests that in cold weather, only that portion of your canister that is propane will burn. If you've got a 100g canister of 70% butane and 30% propane, 70g of your fuel would never burn and would just sit there essentially useless in your canister. This is not the case.
Well, if fractioning is "off," then what is the case? The short answer is that for the typical canister stove, more gas will burn than just the propane -- but you may still get some unburned butane left over. Want to know how it all works? I invite you to peruse my latest blog post: Gas in Cold Weather: The Myth of "Fractioning".
HJ