After last night, I'm pretty well convinced that what is holding me back is the motherboard itself. Reminds me of the old days when overclocking HTT was tough because the boards just couldn't go that far.

HTT multi down from 5x to 4x.
CPU multi down from 11x to 9x.
NB multi down from 11x to 8x.
NB voltage up from 1.175 to 1.225V.
CPU voltage stock at 1.225V.
RAM timings at maximum board supports, DDR2-400 (physical memory is DDR2-800 spec).
PowerNow off.

I crash randomly when HTT is in the 230 range even when the above settings are active. Sample speeds versus stock at crash:
HT Ref: 235 [200]
HT Link: 940 [1000]
CPU: 2115 [2200]
NB: 1880 [2200]
RAM: DDR2-470 @ timings more relaxed than spec for DDR2-800.

The only thing overclocked at this point is the HT reference clock itself, and it's still crashing. As such, I don't think vcore is going to save me. I've got a fever, and the only cure is not just more vcore but a new RS800 motherboard this fall. It's too bad I can't just blow and trace bridges these days on the CPUs to get the multiplier I'm after. I wonder if it's possible to do a pin mod.