as far as the first set of specs you listed with two 12 volts rails listed @ 18 amps each:
18*2=36amps*12volts=432watts/600watts=72% of total wattage.
AFAIK any PSU that cannot deliver 80%+ of total wattage on the 12 volt rail is not desirable since most computers now a days draw most of its power from the 12 volt rail.
Thanks a Lot. This makes sense, I understand now.
Does this mean that even a 500W rated @ 22A with two +12V rails, & 80%+totalWattage can power the GTX570 using a one 6pin connector plus a Molex convertor for the second 6pin required by the Card.