Here is a powersupply calculator:
eXtreme Power Supply Calculator
Agree to abouve. Newer go cheap on the psu! That will come back to haunt you pretty soon. It's like buying a sports car and then get an old Wolksvagen bubble engine for it.
Get one from a reknown brand like Corsair, Seasonic or OCZ for ex. A 750W will be pretty future proof.