efficiency has nothing to do with this....
and to cf 2 hd5870,a 600w psu is enough.[ati recommends 600w only,and the y always recommend more than enough aka lots of headroom]

matrix,the reviews that you posted aren't good psu reviews.
bearing in mind that most psus in a single range is a modification of a single design,here's the review for the 750w unit.
http://www.hardwaresecrets.com/article/Coo...y-Review/917/10

as you can see there's too much ripple and noise.if it's a cheap unit like the cm epp,then it's a given but on units with such price you can get better ones like this one
http://www.hardwaresecrets.com/article/Sea...y-Review/954/10

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Added on August 23, 2010, 8:10 pmstill,that's not to say it's a bad unit,it's just that for the price you can get better ones.

This post has been edited by Racerx: Aug 23 2010, 08:10 PM