Paul,
With your data I have calculated the following wavelengths:
rohm: 663.3 nm
Nichia: 407.6 nm
Pioneer: 653.8 nm
All is related to the HeNe which has the only truly known wavelength. So the pioneer comes out as a pretty good diode. Maybe cooled it will go down to 650nm?
I've put the calculations in an excel sheet for everyone's convenience. The sheet takes you step by step through the measurements and gives an idea about accuracy while doing all the math in the background. So everybody who can set up a laser can now calculate wavelength. I'm pretty sure the sheet works but haven't checked it too thoroughly (usually this means I got it 99.9% right). It requires measurement of both 1st and 2nd order images for better accuracy. Hope you find it useful, all comments are welcome.
Edit: The pioneer maybe closer to 660 than it looks from this data due to measurement error. To estimate the error, multiple measurements can be taken...