First impressions

[deviousalet]

The amount of power being used by Phantoms, and to a slightly less extent Expert with SAM, will depend entirely how much low frequency information there is in the music you are listening to, and how loud you are playing.
The only time they will be taking a constant amount of power will be in standby.

The figures for the B&W and KEFs playing music would be varying not fixed, and with SAM would vary a lot if there is the occasional deep bass.

I disconnect my kit from the power when not using it, but have never timed how long to boot either my 800 or the Phantoms, though I guess the Phantoms are quite a bit longer since I have launched Spark and only had 1 speaker showing at first.

Compared to the two Krell KSA 200b stereo amps I used with my active Apogee Divas the Devialets use negligible power, and can comfortably be used in summer

Since you have a D800 and Phantoms you could do the direct comparison if you have a watt meter.
I don't have Phantoms, but was passing on a best-case power figure (wasting all energy in standby not using any to play music). I assume they will use more power when actually doing something. In my own power measurements I saw a little variation (3W) using big B&W N802 speakers, but very little variation using small KEF LS50 speakers. As you say, bass takes power and the B&Ws have some (-3dB@34Hz) while the KEFs have very little (-3dB@80Hz).
If you would please measure your systems that would be great. Even just a stopwatch and powering on the Phantoms would be educational. Thanks.