This is an old thread but I noticed it wasn't closed.
The previous answers are incorrect.
The correct answer is:
You shouldn't be trying to mine with a 6670. If anyone else finds this page, do NOT mine with this card. Most likely you are spending more money in electricity than you are making back.
Due to ASICs GPU mining is already being squeezed to the max and only really becomes realistic in fringe altcoin mining. But thanks to scrypt asics and god knows what else in the pipeline there is no point competing unless you have some of the top gear.
if you are dead set on wasting your time/money and burning out your old graphics card, here are the ideal settings taken from the scrypt mining hardware comparison:
- -I 18 -g 1 -w 256 --thread-concurrency 2400
That will net you an average of 127kH/s.
For comparison a top of the line card will net you an average of 1,500kH/s.
Keep in mind also that not all vendors are equal, a powercolor card won't be nearly as powerful as an equivalent EVGA or XFX.