I've been quoting 10-year-old numbers on fuel usage and alcohol vs. isobutane canisters for almost that long, but I recently found updated numbers, from much more extensive testing, on Hikin' Jim's Adventures in Stoving, which I've found to be an excellent blog on all things related to backpacking stoves:

Which is lighter? Alcohol or gas?

How much canister gas do I need?

As Jim points out, his numbers are estimates; you really need to do your own testing based on what you actually use. Remember, if testing at home on your patio, use water chilled in the refrigerator to approximate cold mountain spring water. Do at least part of your testing in cool, windy conditions if you can. With (I hope!) cooler weather on the way, we're going into ideal testing conditions!