Gtx 560 ti hawk ( SLI ) and power supply needed

[hasnol]

i plan to add another gtx 560 ti hawk. what is the power supply needed to support my system?
how about the performance compare to a single gtx 580?
is there any typical problem for SLI?
thank you guys!

 

[hasnol]

i have corsair CX 600.. i think not enough..
is there any problem for SLI?