I take it the 3800 series clock down in 2D mode to save power right? I don't think the 8800GT is capable of this, I believe the 2D and 3D clocks are the same.

This may explain why the 3800 has much better idle power consumption, but is around 8800GT levels under load.

However, anyone with a 8800GT can use a 3rd party program to set seperate 2D/3D clocks, which should bring the idle power way down.