newer AMD64 newcastles and the like seem to handle high vdimm fine as i haven't seen or heard of newer cpus dying at all with 3.3-3.6v vdimm pumped into them. Now whether particular memory can handle it really depends on memory.
Winbond BH-5/6 handle high vdimm well 3.0-3.6v
Winbond CH-5/6 don't handle high vdimm well
I think 2.9-3.1v should be fine for most memory.