I suggest try value like these....I'm pretty happy with them.....temperature and fan are quite and power usage is about 180W x card.
Voltage is ok on my cards but on yours could be different .....you have to try go down with Voltage until it doesn't work anymore.
I suggest using MSI afterburner to find best setting and yhen flash them with atiFlash+VBE7


GPU 1: 625.1 / 629.2 Kh/s | A:26823  R:231  HW:0  U:31.28/m  I:13
58.0 C  F: 51% (2055 RPM)  E: 915 MHz  M: 960 Mhz  V: 0.981V  A: 99%  P: 0%