I wouldn't think he would have to touch the voltage on that prescott just for a 200mhz OC. I wouldn't recommend upping the voltage much anyway because that thing puts out so much heat already.
I'm with elitelilnoyd and arronkelly on this one. Sounds like you don't know how to overclock properly and shouldn't be messing with voltages anyway. Prescotts don't need more voltage unless you O/C ~600mhz or more.