Mining Darkcoin on a ATI 5870

[slacky741]

Hi Guys,
I have been mining bitcoins on an Antminer S1 for the last couple of months which i pretty straight forward and doesn't really require much setting up. I have just recently decided to give mining some Darkcoin a go using my ATI 5870 card. I have managed to get it set up in sph-sgminer and it is mining with my pool at about 1.7Mh/s however i just saw in this forum post h--ps://bitcointalk.org/index.php?topic=475795.240 that someone with the same card is getting 12.7mh/s which is a huge difference and i was wondering if im probably doing someone wrong?
My config in sgminer is:
sgminer -k darkcoin -o stratum+tcp://drkpool.com:3333 -u USERNAME -p PASSWORD

Im very new to this and any help would be appreciated

Thanks

[Catmoonglow]

Yesterday I tried to setup my GPU to start mining darkcoin, i tried using both sgminer and cgminer but both are throwing back invalid value passed to set_worksize.