I'm actually struggling installing/downgrading to sdk 2.1 and 11.12 from 12.8 and sdk 2.7 under W7 x64. CGMiner 2.7.5 didn't like the sdk 2.1 and said that no devices was found/usable even though 2 lines before it lists the sdk.
try grabbing cgminer 2.5.0 and see what happens. The newer miners work better with the new hardware 79xx series. Older miners are better with older software.
5830 = 950c/300m/1.05v = 315mhs
5850 = 925c/300m/1.05v = 385mhs
5970 = 805c/300m/1.05v = 375mhs/core 750 total
6870 = 950c/850m/1.162v = 297mhs newer sdk and driver-2.4, 12.1 i think that is what this one is set at