7970m is basically under-clocked desktop 7870
desktop 7870 at 1000/1500 MHz gives about 400kH/s ...
https://github.com/litecoin-project/litecoin/wiki/Mining-hardware-comparisonso 250kH is maybe appropriate, probably not possible to go over 300
in guiminer try to use defaults for 7870 not for 7970
try thread-concurrency 15360 or 16384
maybe also try cgminer instead of reaper to see if there is difference
BTW what is your GPU temperature during mining?