Maxwell is very efficient. That is no joke. It is real.
The issue is the high clocks on the 28nm node. Nvidia was aggressive with their clocks. These are the highest clocked 28nm chips ever but even still, everything stock is perfectly under control. Very impressive power consumption.
But then their are AM vendor OC models with custom bios. This is a place where binning comes to play. You are already at the edge of the limits and some chips require more than othrts to go that much further. Most vendors try to put the best binning chips in the custom oc cards and this allows them to get that much more performance without a huge spike in consumption. They pick thru the chips.
Honestly it looks like msi is doing something very different. My feeling is they arent binning nore trying to choose the best chips. They are cranking up the values for the worst case and calling it a day. This isnt something new at all. This is why kepler had a voltage lock so low. Cause vendors can make their chips look very very bad. Msi is doing something very diffetent than the others. Maybe it saves them money idk. But their methods should not be something you judge maxwell by