You should be fine with just one. I use the 220gr because that's the easiest to find here, and I use around half in 5 days. I also use the pocket rocket II. I'm planning a 10 day hike in November, and only planning on taking one 220gr can. I heat water for breakfast and supper (freezer bag or mountain house meals), along with coffee in the morning and usually hot chocolate in the evening. Taking a backup such as solid fuel is not a bad idea either. The only thing I don't know about is how the altitude affects usage, as my hikes are not very high. Seems like with less oxygen you're going to turn it down and use less fuel, but at the expense of taking longer to heat your water, so probably about the same fuel usage overall. From what I've read elsewhere it's way more important to warm the canister if it's cold than altitude being an issue.

I've often wondered what freeze-dried meals taste like with cold water, but I've never ran out of fuel LOL.

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