Max NB and PLL voltage

Hey ther.
I have a Asus P5E3 Premium X48 mobo.

Im trying to oc my Q9450 to 4ghz but the board refuses to reach FSBs of over 475 (thats using setfsb in windows, cuz at that 468 it wont boot)

So i was wondering what would be the max voltage i could get to my NB but not burn it, also whats a good PLL voltage (im currently at 1.74v)

Im cooling my pc with an AC unit, current temps are as follows:

CPU Idle: 21ºc @ 1.4v (measured in cpuz, remember its 45nm :P )
CPU Full Load: 34ºC
System: 14ºC

And i measure other components temps, they wont even get hot.

PS: i know the problem is the NB and not the RAM or CPU cuz i lowered the CPU multi and lowered FSB:DRAM ratio to a low value (1251mhz on OCZ platinum edition 1333mhz) and tried raising FSB but it would still get lots of errors in memtest / prime

Currently im running it fully stable @ 3.6Ghz @ 450FSB and NB @ 1.43v and PLL @ 1.76v

I hope you guys can help me out this time