A cx600 would be useless to over clock a s3! I need 2 cx750 to have two overclocked s3s
Why do you say that? Have you actually run an S3 with a CX600?
Even if an OC'd S3 draws 450w at the wall, it only represents a 73% load on the CX600.
That's not really how power supplies work. Overall wattage is not the representation of how much power it can give on the 12v rail.
The cx600 has a 46A on the 12V rail, this is 552watts. That's 81.5%load without the added power draw from the wall minus efficiency of the power supply.
Seems it only comes with 2x PCI-E adaptors, so you would need molex to PCI-E or sata to PCI-E if you wanted to connect all 4.