Why bother
what does it matter who's 2TB drive is sucking up the least wattage, they are all under 10W these days (green/energy efficient ones anyway).
I've got an 800W PSU in the back of my PC, the watercooling tower gets too hot to touch. The energy wastage isn't in the drives is the vast quantities of heat that performance components (CPU/NB/GPU) put out.
When it comes to disks we should be interested in how much they can hold and how quickly they can deliver it.