So would I be right in saying that the Antec TPQ-850 TruePower Quattro 850W PSU would be no better for overclocking, despite being very powerful, because its same four 12V 18A rails would provide the same limiting factor.

+3.3V@25A;+5V@30A;+12V1@18A;+12V2@18A;+12V3@18A;+1 2V4@18A;-12V@0.5A;+5VSB@3.0A

+12V1 > EPS12V 8-Pin and ATX12V P4 connectors
+12V2 > 4-Pin Molex, SATA and Floppy connectors
+12V3 > Main ATX, 1x6-Pin PCI-Express and 1x 8-Pin PCI-Express connectors
+12V4 > 1x6-Pin PCI-Express and 1x 8-Pin PCI-Express connectors