Power efficiency
What you're looking at is the power-draw at the mains when the systems are idling. The top four numbers represent systems without the discrete graphics card in, while the rest house the HD 6950.
34W is a yummy figure for a complete rig with 4GB of RAM and a potent CPU at the helm. Of course, you're not purchasing a system to leave it idle, so how about some all-core load through wPrime.
The IGP-only boards still do best here, and both Sandy Bridge chips are relatively power-frugal when under the cosh.
