you can go higher, but first you need to raise your memory voltage. I'm guessing it defaults at 1.8v (for memory)
What you want to do is take your memory voltage to 2.0v (not your CPU voltage, 2v on a CPU will kill it). keep the CPU voltage at 1.385v when you have done this and see if it is stable.
Im not sure whether I can control the memory voltage, it says something about "Overvoltage DDR2 control" and then has options from "0.1+-" to "0.7+-".
Thanks