Originally Posted by Atomfix
Using my watt meter that my computer is plugged in to, my computer does 30-35W less when my 7950 goes in Zero Core.
The X1300 I have doesn't have a PCI-E Power connector, and it's very small.
The 7950 in ZeroCore pulls 15W from the 12V rails, while the X1300 pulls 15W from the PCIe connector while idling.
Seriously, for the hassle involved (switching video outputs, having two cards inside the computer, and having an additional fan working), it is not worth 25-30W.
I used to run a dual card setup for that purpose aswell, a X1600 Pro with a 8800GT and later on a X1600 Pro with the HD5870, and after using it for a few weeks I concluded it simply wasn't worth it.
It turned out to be more efficient to simply set up deeper sleep states on the Thuban (modifying the idle state to run with less voltage and at less corespeed) to achieve said power savings than switching GPUs.
And I'm talking of a much larger power consumption difference between my case and yours... The 7950 eats WAY less power at ZeroCore than my idling HD5870 did,