Your experience sounds fairly typical for alcohol stove performance. Where I live, at 3200' altitude, I can get a rolling boil with two cups of 50°F water in still, 70°F air in a bit under five minutes. I get a total burn time of about seven minutes with 0.8 oz. of fuel. High altitude will reduce the performance a bit but usually, the effects of altitude (lower partial pressure of O2) are minor compared with the lower temperatures and wind you tend to get with it.
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May I walk in beauty.