Hello,
I am afraid, I don't have good news. I have been in the service for the last 4 hours. They tried another 2 UD5's, one X58A UD5, 2 UD3R's , different CPU's, different RAM's, different video cards.
With each and every motherboard, the same, RAM was not fully detected on restart and when trying a cold boot the motherboard would not boot at all. They had to wait for 3 minutes to make the system bootable again.
The last thing we tried was swapping the motherboard for an Asus P6T.
The results?
System booted just fine, RAM was detected correctly in every single reboot and no problems appeared when booting.
Sorry, but I think that the motherboards were the culprit here. I did not want to have my GB exchanged for an ASUS at all, believe me. However, right now I have lost faith in GB. In the end of the day the service department contacted the central offices and they responded that this is a known problem with Gigabyte motherboards and that the reason it is not so well-known is that there are very few customers loading their system with 12GB of RAM. Obviously these motherboards cannot handle it.
I am very frustrated, because I have been counting on Gigabyte motherboards for quite some time. However my system would not work at all if I didn't switch to the Asus.