To eliminate your ram as the problem, try running your ram at 2.1v, set the timings to 5-6-6-18, and set your ram tRFC timing to 54 (my ram defaults to 36 tRFC on AUTO which causes instability on higher o/c), and DISABLE your Transaction Booster to lower your Performance Level for testing.

On my Asus P5K-P/E8400 system, increasing the VTT (FSB Term Volt) seems to reduce stability. I run mine at 1.1v @ 4320 MHz (480 x 9), with 1.5v PLL, 1.4v NB, 2.1v ram. I believe Intel's maximum recommend VTT is 1.115v.