Power consumption

GTS250 Maximum Graphics Card Power (W) = 150 Watts ;
HD6850 Maximum Graphics card power (W) = 127 Watts ;

so yes;

yes it uses more power and gives low performance then hd 6850.

To be sure, what do you want exactly?

The original 65nm version of it probably does, but the newest 55nm version probably uses similar if not a touch less power.