You should lock your PCI bus...

And have you locked your memory timings (RAS-CAS-TAS...)?

That's a good start though :D

My CPU is a 3400+ and has a default of 2009mhz core.

With my PC I'm running a VCORE of 155 + 104% (1.61v), an FSB of 230mhz and a 11x mult. I have also put a divider in my RAM, and set the RAM timings.