yes, you will need to raise voltages of different components.
are you using that 667mhz pair of ram with 800mhz, if yes then either use x1 or x1.66 multiplier for memory and latency settings of 667 (x1.66) or of 800 (x2) respectively (use cpuid to get your ram's settings).
and keep experimenting different combinations, and also use prime95 to test stability and max temps at those clocks.
in case of no booting you will need to clear the cmos (using jumper or switch or taking out the battery)
e8400 overclocking video...