Decided to buy one, and was able to do some measurements (European 230V situation), so might as well report the results here (which turned out even better than I expected):
No cables connected:
- Power adapter only, with router turned off: 0.2 Watt
- Out of the box, no WAN (modem) or LAN ethernet cables connected: 6.3 Watt
Internet (=cable modem) connected:
- No ethernet connection, both radios OFF : 5.0 Watt (sometimes even 4.9 Watt)
- No ethernet connection, 2.4GHz ON, 5GHz OFF: 5.7 Watt
- One 1G ethernet connection, 2.4GHz ON, 5GHz OFF: 6.1 Watt
- One 1G ethernet connection, 2.4GHz ON, 5GHz ON : 6.9 Watt
I didn't really test with substantial traffic. All of the above values were without any wired or wireless traffic (except perhaps for some light background traffic).
Bottom line:
Bottom line for my situation (one 1G computer connected, 5GHz radio OFF) is 6.1 Watt, going down to 5.7 Watt when my computer goes to sleep (i.e., ethernet connection goes down as well).