https://en.bitcoin.it/wiki/Mining_hardware_comparison

A 7970 can run you anywhere from 625 to 925 MH/s which at the current rate contribution/pool rate)*3600 or 625/25,000,000*3600 = 0.093 BTC a day Which means you'll get roughly 2.81BTC every 30 days.

Correct me if I am wrong!