I have the same issue - but with a twist. One AC68U brand new but manufactured in 2013 overclocks just fine to 1000/800. Another AC68U manufactured in 2014 won't let me overclock the DRAM off the stock 666 or it goes into reboot loop mode. I can do 1200/666 on the new 2014 model. Same hardware revision on both units, same stock firmware shipped with the units as well. Both are running and shipped with the Bootloader version 1.0.1.6. Odd....