My well used E8400 C0 needs very close to 1.40 volts to be stable at 4 GHz but most E0 chips can run 4 GHz with less voltage.

It might be your memory holding you back. I'd drop the multiplier down to 8 and test again and make sure that your memory can run this speed reliably at that memory voltage. I tend to like 2.00 to 2.10 volts for DDR2 but every stick is different.