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Either one would work fine. If budget isn't a concern get the 750w Gold rated. If it is get the 620w one. If you re thinking of a future SLi or crossfire then you might be able to get away with 750w(depending on other specs and overclocking) but I'd probably recommend atleast 850w for that.
Well if you have a bigger budget, then the ones you mentioned are quite good. A decent 600-700 watt PSU would be enhough.