You can likely lower the power usage and definitely the temps by underclocking the mem clock. With this algo it doesn't seem to need a high mem clock like scrypt. I have the mem clock set to under 400mhz on all of my rigs with no loss of kH.
On this card, lower memclock have an effect on hashrate.
On my 6950 1Go ( with faster memory than 2Go models ), memclock @800 have same result than @1300 ( stock value )
If i lower more than 800, GPUZ show me memclock is forced @ stock value.
Are you sure your memclock is really < 400 ?
And my GPU actually serve for heating my basement, so i don't really search heat performance
