A lot of the gigabytes are having problems with the 8.00x memory multi. I suggest backing it down to 6.66x and upping the HT. Ref. Clock to the desired speed.
(Applies if that is what you are using)
Also, this may be a little weird...but try LESS voltage on the ram. Start at 1.65V and increase. See if this can get you stable at the settings you are looking for.
Second, leave the ram Unganged...no need to decrease your performance.
Third, Increase NB Voltage (NOT CPU-NB) to the max your board lets it. This greatly helps with ram stability.
Lastly, it would help if you could give me insight on what IC's your ram uses.
PS. Memtest is good for initial testing, but will not pick up every error. Prime 95 blend for about 3 hours is the best way to guarantee ram stability.