You are overclocking your memory. That may be limiting your CPU overclock. You are running DDR2-800 RAM at 860 MHz. Adjust your memory frequency so that the memory is running two times the FSB frequency. At a 344 MHz FSB freq, your memory clock should be 688 MHz.
Intel's recommended max vcore is 1.3625 volts. Intel's absolute max is 1.45 volts.
Wolfdale voltage specs:http://download.intel.com/design/processor/datashts/318732.pdf
page 17 (you can learn all kinds of stuff digging through datasheets)
And if you still can't push the core speed higher, you may be limited by your motherboard or the CPU chip itself.