http://packafeather.com/xlstove.html
http://www.traildesigns.com/stoves/caldera-cone-system
I decided to put my theory to test to see the results.
For both stoves I used 1oz of metho (measured) and 500ml of water at room temperature. Wind was not a factor as both were tested in my trusty kitchen sink under the same conditions. For both I measured time to boil in the cone with the lid on the pot. Once boiled I removed the cone off the stove and let the stove continue to burn out of fuel. I also noted this time.
First up I tested the 12-10 stove in the cone. It took 6min 31sec to bring the water to a rolling boil and the flame finally died at 11min 30sec.
I then tested the packafeather XL and it took 4min 48 seconds to get to a rolling boil and the flame died out at 7min 42sec.
Some comments. Firstly the 12-10 is a lovely stove. Its robust, well made and well designed. Its got a well focused flame and performs well with good fuel economy.
As for the packafeather...well there's nothing scientific here I just love this stove. Its absolutely delightful for a metho stove and packs away neatly. Now it obviously burned hotter and thus was less fuel efficient but the one thing I didn't mention was this stove has a flame control. For the purpose of this test I had the stove opened right up going all out. There is a brilliant simmer ring on this stove that dials in and out with a screwing mechanism. I will conduct further testing to give an exact time but I can tell you this stove will simmer for ages. I have cooked a risotto on it in field and it cooked away happily for over 20 minutes (with slightly more fuel).
12-10 stove weighs 16g
Packafeather weighs 45g
Now obviously if your a gram weenie and want minimal weight with an efficient stove the 12-10 is the way to go. I personally feel the extra 29g is no issue especially considering I have got good flame control (ie can go for either hot fast flame or simmer and more efficient) and the ability to snuff the flame out and save fuel (the 12-10 cannot be snuffed unfortunately).
So verdict for me is ill be using my XL with the cone in field. Note I also own a starlyte stove and will compare it to the 12-10 (I've already done a test at home before so I know its slower than the XL).
Some pics

12-10 on left XL on the right as they would be stored


Ready to put in my pack with pot, silicone mat, XL stove, spork, cup, fuel bottle, caldera cone and lighter

NB the case of the cone is food grade and can be used as a cup and bowl. I will most likely ditch my sea to summit collapsing cup.