WC doesn't use as much power to cool a card. As my 5970 fan failed, I used an undervolted pump with a passive radiator (a huge 360x360mm one) : it's probably the most efficient setup you can get, it only consumes ~1W.
For comparison, IIRC, depending on actual airflow around the card, the fan consumed between 10 and 20W to cool the 5970.

My GPU temperatures are lower than with the fan (when it worked correctly) too, and power usage is going slightly up with the temperature, so it should help a bit.