efficiency has nothing to do with this....
and to cf 2 hd5870,a 600w psu is enough.[ati recommends 600w only,and the y always recommend more than enough aka lots of headroom]

Exactly. This thing I already posted last time too.
Actually, one should know that CM GX is APFC and 80+ but they're cheaper than CM Real Power(also APFC and 80+). So, you know...(quality and performance) I think I no need to explain further already.

For me, when choosing PSU, I would avoid CoolerMaster Brand(even some of it's models are great).
Corsair will be avoided too due to overprice.