@ TS: don't concern too much about this efficiency ratings...they are just numbers telling you how your psu operates at respective loads vis-a-vis the power it draws from your wall and the power it delivers to your components...
the MORE important thing is the one you don't see there bec. its often not included by the manufacturers: the PSU Derating Curve...the effects of temperature on the performance of the power supply...it is measured as Watts per degree. For example: "2W per 2°C" would be a "derating curve."... what this means is if a power supply was rated at 500W maximum sustained output at 20C, then it's maximum sustained wattage capability is reduced by 2W for every 2°C it's temperature is increased...so at 50C, the maximum sustained output of this power supply may only be 470W.
mao ni dako ug effect nato considering nga taas ang atong ambient temp & most of us are not using aircon most of the time nag gamit sa pc...
you can ask for the derating curve from FineUpgrades...i think they can get the info from Silverstone...ma-apil pud na sya in some reviews for psu...
btw...i have the same psu as yours...works as expected...just like my other 4 Silverstone psu's here...mao ni akong gipuli sa akong HEC Cougar 700w nga na RMA(thru PCQBuys) kai naka sunod sa akong 500GB Seagate sata2 + XFX mobo + Gigabyte G31 mobo...funny thing kai ni tawag ang technician sa distro sa HEC (PCTRENDS Manila) and iya kung gi-ingnan nga ok kuno akong psu nga gipa rma...2 hours na kuno niyang gi test running pa iyang system...suddenly ingon sya "hala umusok yung board"

they sent me a new one(HEC COUGAR POWER 700W) after waiting for ONE MONTH & 2 WEEKS...i promptly sold it for 3k...