Successfully OCed my E6750 from 2.66 to 3.4GHz. Running well , CPU Vcore and temp fine.

I left the voltages set to auto in BIOS and the FSBT has been pushed up to 1.5V which is about 0.22V above start voltage (17% increase). Also the Northbridge voltage has risen to 1.57V which is about 20% above start level.
The Northbridge is now running at 48C when running 3DMark06. I haven't installed watercooling for the NB and its relying on general airflow in the case - I have a Scythe Ninja on the CPU which works weel for the CPU temp but doesn't reall yhelp with the airflow around the NB.

Are these voltages OK for the Mobo or am i in danger of frying the board?

you would be much better off learning to change the volts manually when over clocking. Most boards tend to "over volt" when left on auto for the sake of stability. You should be able to lower your temps a bit with a little patience and tweaking. I however I don't believe that 46c
is that bad for the northbridge. I'm pretty sure it's safe to 70c but you wouldn't want to run that temp for the life of your machine or it may expire sooner. If your concerned I would recomend putting in a side fan
or a fan that blows directly on the northbridge/ram moduals

deranged,

It is safe to start as with the CPU? i mean, lowering the voltage to the bottom and test from there and raise it as needed?
What application could be good to stress/check NB/SB? I guess i should use something that push my video card? prime work also for NB/SB? i dont know!