should up vcore to 1.550??
Now your going to find out why we said cooling is so important.

Your CPU will be fine at the highest voltage your MB provides, that is if you have proper cooling you should be able to do a vcore of 1.6-1.65 with your HSF, ???? maybe...

My XP 3400 is @ 1.525 vcore and 2.5 ghz so your in the right ball park I don't want my fan to sound like a Jet plane so thats where I keep it.

Also like I said before, FSB is where its at so work on upping the Ram and less emphasis on the CPU.

Anywhoo to answer your ? 1.6 range vcore should be ok, check the temp and work on the FSB.