I saw a spreadsheet that did this a while back. It calculated "Watts and/or BTU/H to the pot". I can look for it and send it to you again if you like.
I think this is the best way to rate a stove because this one number makes comparison's easy. When people publish boil times, too often they leave out one critical parameter or other. e.g. starting temperature, quantity of water etc. Even if they include all the parameters, it's still difficult to make comparisons because they all use different starting temps and water quantities so additional calculations are required.
On the other hand, it's easy to compute boil times for various conditions once you know the Watts to the pot. Measuring Watts also speeds up testing because you don't need to wait for a boil for most types of stoves. (wood stoves are an exception because the wattage varies wildly and some averaging over time is necessary.
Finally, true fuel efficiency can be computed if you know how much energy is in the fuel you're using. Fuel energy content tables are available on the internet.