There is a huge difference in the strengths of various steels but less spread in the stiffness. I have no idea what steels Kirkham uses for the regular chassis or the stainless chassis I could not find it on their website. Here is a good link to MIL HDBK 5, which is an Aerospace materials design document. If you look in chapter 2 you will find the properties of virtually all high grade steel and CRES (corrosion resisting steels).
http://www.grantadesign.com/cgi-bin/...IL5-H.xml&br=3