How high is too high?

I read a review that if your memory wont post at 2.8-2.9volts, it wont go any higher even though its at 3.2v . First off, is that true? 2nd, is setting my Vdimm at 2.8v or higher dangerous for my memory? Keep in mind i only have PC2100 memory but i really would like to get to 166mhz.

EDIT* My config is 3 x 256mb