I haven't played around with the settings as much as some of you, but my best speed (and OC) is around 648 S/s.  Power lim at 120%, +140 core, +500 mem.  Temp gets as high as 85c.  I think efficiency was somewhere around 2.x - Core was at around 1980 MHz while mem is 5508 MHz.  Power draw was around 275W I think.  Fan was at around 80%

I found the best efficiency I could do was just leave it at base clock (1480/5005).  Dialed the power lim it 63% and leave the core and mem clock at +0.  This leaves me with 540 S/s at 3.4 efficiency, 72c (lower fan speed - 42%) and power draw of 157W.