I had the same issue where 6Gb of 1600Mhz Gold Version on my Asus p6t deluxe v2.
MemTest and CPUz could see all 6Gb but the BIOS and Windows 7 64 could not.
So, I manually set the 1600 frequency and 8-8-8-24 timings in the BIOS, systematically rotated the DIMMs in the various channels to assue it was not a bad channel and/or sitck and still no luck.
I then looked at the QVL in the manual and apparently, OCZ is not a qualified vendor of the 3x2Gb version @ 1600 MHz. So, I RMA'd to newegg for a trio of slightly more expensive, and seemingly similarly performant Corsair sticks and they worked out of the box as advertised - no manual settings needed.
Guess next time I'll read the QVL more carefully.