"But Conroe and Woodcrest share the same shared cache architecture, don't they?"
AFAIK, the two chips are indentical, except maybe for cache size. And yeah, that would be the case. I don't see how a shared cache could affect things, but who knows? Other possibilities would be things like SSEx and the FSB. SSEx might be used for some operations in a soft raid, but that wouldn't explain the Woodcrest results. It could be that the FSB glitches under the load of a RAID controller.
It is just odd.