Not shure about 7870, but on my 7850 i getting ~387 kHash/s and i think i can get more (experimenting now). I'm using 2.11.3 cgminer.

UPD. Try to use configs like here (find your GPU in list) https://github.com/litecoin-project/litecoin/wiki/Mining-hardware-comparison . You must get about 400 kHash without any problems.