Intel's recommended max voltage is 1.3625 volts for the 45 nm CPU's. You can find all of this with Google.
Your problem is that the CPU voltage in the BIOS is on AUTO and you have no idea what EasyTune is doing. From experience, it is overvolting and that's what SiSoft is picking up when you run it.
Learn to use the BIOS. It's a little more work, but it will give you complete control.
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1 http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guidehttp://www.tomshardware.co.uk/forum/page-245679_11_0.html
The relevant part of the P35 BIOS is very similar to the X38.
Keep your temps under 70 C.