Interesting results here. Nvidia insists that the GeForce GTX 275 is based on its 55 nm re-spin. The data in GPUz would seem to concur, as would the twin six-pin power connectors on the reference board. However, at idle, the GeForce GTX 260 Core 216 and GeForce GTX 275 both use more power than the GeForce GTX 285. Applying a full load on the cards sorts them back out in the order we’d expect to see.
Representatives at Nvidia explain that this isn't altogether uncommon behavior, as variance from one GPU to another will give you power consumption numbers that span a given range.
Compared to the Radeon HD 4890, the GTX 275 demonstrates similar idle consumption and markedly lower load power.