I have a GTX 670 and added a second GTX 670 because I bought a larger monitor. My memory used to run at 1600Mhz but now it's only stable at 1333MHz. Do you know what could be causing this? Could it be related to the power supply? I currently have a OCZ 700 PSU.
Here is my other specs. I7 2600K at 4.2Ghz 4 x 4 GB Corsair RAM 1 x 256 SSD 2 x 2 TB traditional hard drives in a RAID 1 configuration 1 x standard SATA DVD drive
More aboutmemory runs slower adding
since you have 4 ram sticks i would raise the voltage a bit and see if that helps it run at 1600