Bill et al.,
I spoke at length with IDFL yesterday about down testing.
None of their tests stimulate real world testing. 900 fp in a test is going to be a pipe dream in the field, because they steam wash and dry the down to nearly zero humidity before doing the test. Ironically, this most recent iteration of test methods was designed to determine the maximum possible fill power for down rather than what it will look like in the field.
Interestingly as a side note, we did some 900 fp testing of down a few years ago on two manufacturer's 900 bags. We cut the bags open and sent them to IDFL. Neither made the claimed 900 spec (they tested 830-870 using the steam method). What was more dramatic was that when each down (which clearly came from different sources as evidenced by visual inspection) was subjected to 50% humidity, the differences were pretty dramatic. One bag tested at 770 fp, the other at 680 fp. It seems that at least these two sources of 900 down had feathers in it that were not resilient in response to humidity.
The kicker is that we ran the same test next to down taken from a manufacturer's 750 fp bag. at 50% humidity, the fp was 720. Why? It had more feathers that were stiff enough to preserve the loft in moist conditions.