I7-920 overclock question - weird thing I just discovered

So I'm learning how to overclock my Asus P6T, but what's become truly bizarre is that the memory I originally ordered from Tiger Direct was 12GB Corsair XMS 3, with a speed of 1333MHz with a timing of 9-9-9-24. But the BIOS on my computer reports the memory as being 1066MHz, with timing of 8-8-8-20. This is not the memory I originally ordered, and I tracked down my original invoice to prove it. Now the guide I was reading is teaching how to OC with the RAM at 1600MHz, but with mine being 1066, could this possibly affect the maximum speed that I would be able to OC the 920 at? I'm quite certain I could get it to run at 3.5 - 3.7 with no worries, but I'm not sure I could go beyond that.

This is the setup:

Corsair Graphite 600T
Intel Core i7-920
Corsair XMS3 Tri Channel 6GB PC10666 DDR3 Memory (x2 for 12GB)
Western Digital Caviar Blue 320GB 7200 RPM (soon to be replaced with Samsung 470 128GB SSD)
Western Digital Caviar Green 1TB 5400 RPM
Thermalright Silver Arrow
Dual EVGA GeForce GTX 550 2GB in SLI mode
Plextor B940