I wonder the same about P35 vs 38. I have tried everything with this chip and it needs a lot of vcore to be stable at high speeds. Like I said, >1.43v to get 4.2ghz prime stable.
So is it the chip or the chipset? Hmm, I have been tempted to pop this in the P5E but I want to return for refund so I dunno.
Aren't there some sponsored benchers out there who can confirm or deny the performance diff between P35 and X38 by using the same chip in two boards with settings as close as possible?