Captn: Orthos is just a fancy GUI wrapped around the Prime95 code. I prefer
Prime95 version 25.6 because I think it's a more recent version of Prime95 than what Orthos is using.
I put a link to the RealTemp docs in the post just above yours Captn. It talks about the Calibration procedure there.
For Prime testing an E8400 at 3600 MHz I'd start at 1.20 volts as reported by CPU-z under Prime load. I think the really good 45nm Dual Cores can run at 4000 MHz with about 1.25 volts so for less MHz you might be Prime stable with about 1.20 volts.