Fishmonger,
With almost any brand of canister gas, you're going to get significantly better cold weather performance if you use the canister upside down. However, some brands of gas are better than others.
thanks for posting the mixtures - looks like I should stick with MSR and Jetboil for the higher propane content if I leave the Helios at home. The Jetboil Sol is so much lighter for solo trips, that unless I am about to melt snow for a week, I will come out ahead in terms of weight, even if some fuel stays in the canisters. there's always the hand warmer plus sock trick or just to put the canister in your sleeping bag or inside coat pocket for a few hours.
Primus clearly is not what I'd want to bring in winter, and even in summer in the Sierra, they may not work that well.
We have an REI in town and their prices match what you found.
