1648mhz RAM is enough to cause instability. You can try increasing the DRAM voltage to 1.55-1.6. Don't exceed 1.65V to be safe.
Secondly, increasing the CPU speed will need voltage. 1.325V is obviously not enough. Try 1.35V?
I highly recommend you go over some overclocking tutorials to familiarize yourself with the proper methods of OCing to avoid future issues.
This might be a good starting place:http://wolframpc.blogspot.ca/2012/01/guide-to-overclocking-part-1.html