You should try another pool ( maxhash PPLNS) or maybe try solo mining luck with that hashrate i would try ETC solo mining for a week. With ethermine pool you want have the opurtunity because of to many miners to see what can cards do( to many stale shares)Solo pools are more optimised then PPLNS pools. Im only solo mining. You must make calculation on dificulty (TH!!!) your cards find on 24 h basis, but that you want find on ethermine. You should try solo mining pools (maxhash, 2miners,altpool,coinmining, clona).