Nice work.
The output is actually higher than I would have expected--I poked around the P7 datasheet for a bit and estimated the actual output would be somewhere in the ballpark of 600 lumens.
900 lumens is actually the high end of the 'typical' P7 luminosity spec. The P7 used in the Magicshine light is from the 'C' luminosity bin (rated at 700-800 lumens @ 2800 mA of current). Actual output is even lower, since the Magicshine drives the LED with 2400 mA of current, not 2800 mA, and the junction temperature is well above 25 C (elevated junction temperature also causes output to drop).
I was considering doing some measurements of my own (I'm a PhD student in an atomic physics/optics lab) but I don't have access to a luminosity meter, just a power meter--I would have had to do some sort of conversion from watts to lumens based on the LED color temperature or something.