In fact, it does have a bit. Although I'm not sure if ECO is present in X3D models.
If you think of it on a graph, the curve will be lower and as such, at the same load and frequency it should have less wattage as it won't apply the same amount of voltage in a given moment.
Of course this depends on so many factors that trying to myth bust it, is quite hard.
On average, With ECO 105 enabled I can see a very very tenuous slight difference in wattage on a 7950X
In the end I would curve optimize or undervolt it myself with a negative offset value like -0.1, this should visibly lower the wattage.
The Englishman