If you are already using a 600w with success, then there is no reason to discontinue this, especially with a Corsair branded item. But having said that, a little bit more wattage, might help for the future. What I would not do, is use a less powerful psu, like you intend doing.
I obtain my psu units from eBay, and never had a complete failure yet. Usually if the computer was originally supplied with a 350w psu, then for the small increase in price I normally replace with 500w units.
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