Some Sandra mem comparison at DDR 400....(CTL Samsung, 2.75V)
Epox 4PEA: 2.5-2-2-6
http://users.on.net/nlinh/HW/4PEA_DDR400.jpg
Epox 4G4A+: 2.5-3-3-6
http://users.on.net/nlinh/HW/SandraDDR400.JPG
Other boards like BD7-II, IT7, 8PE667 Pro, P4B533-E don't even come close so not worth mentioning

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Edit: that is 97 or 98% efficiency.