to the wonderful world of the Gigabyte x38

Have you set the timings manually or auto? If auto, try setting manually. You could also try relaxing the timings and/or frequency to see if it can pass the tests. The problem may not be the memory - it could be the motherboard (or psu, cpu, etc..).

What voltage are you giving the memory? May be worth checking if the voltage is correct or, if the memory allows, overvolting. Thankfully, the bios hardware monitor does report the memory voltage. Early bios revisions were known to undervolt some memory modules. I remember initially my modules (Ballistix PC8500) were given 1.8v with F3, but later revisions provided 2.2v. Saying that, this was only when auto timings were used. Any attempt to manually set the timings dropped the memory voltage back to 1.8v and I needed to overvolt by 0.3v or 0.4v.

I know a number of people are reporting problems running memory at 1066, but thankfully it's not a problem I have.