I've got a Black Edition HD7970 that churns out ~600Mh/s non-stop @ 79°C. (Win7 x64, 850W PSU, Catalyst 13.1, cgminer 2.10.2, Bitcoin)
Well you should be able to get at least 700Kh/s with that card.
What voltage are you running? That temp seems a bit high for only 600 Kh/s