My RAM is 1600mhz, and my CPU is a Phenom II 955. I was told that some sort of controller on this model of CPU is ineffective above 1333Mhz and I've been having some of the same symptoms that person described, so I'd like to decrease the frequency of the RAM.
My motherboard is an ASUS M4N68T-M V2. I intend to replace it within a few months, I'd prefer to get the RAM to 1333Mhz with timings at 9-9-9-24 before then if possible. Does anyone know how I would do that in the BIOS? Is it even possible on my motherboard? :s
If you look at section 2.2 of your manual it explains how to enter into BIOS to change settings. Once in BIOS, navigate to the Advanced menu. Go through each item in the Advanced menu until you locate the clock controls for your RAM modules. You should be able to find what you want in there. Understand, if you choose timings that are not compatible with your modules, your computer may fail to boot up again. I would recommend you familiarize yourself with and understand how to reset your BIOS if you make a change that prevents your computer from starting. Page 1-18 in the English version of the manual details resetting the CMOS, in case you computer fails to boot after you make changes.
As for the memory controller in a Phenom II 955 being ineffective above 1333 MHz, that is simply untrue. While the highest specification supported when it was designed was 1333 MHz, it should quite easily run 1600 MHz RAM, provided the motherboard supports that speed, and you have both the timings and voltage set correctly for your particular RAM modules. If you are running RAM modules from multiple kits, there can exist timing discrepancies between them.