Looking at the graphs again: I'm wondering if it might be possible to get more light from a LED by running it at less than rated current if your heatsink isn't perfect.
eg. If you get 20% less light output at 70 degrees C, could you get the same light by running it at 450mA and not heating it up so much? Most of these LEDs get far too hot to touch if you run them at rated current so the loss due to temperature must be very real.