Not sure of the tubing, it was designed and drawn to Specialized's own specs. It is oversized, shaped a bit, and the walls thinned down some, but not sure if it's any kind of premium steel alloy other than generic 4130 cro-mo.

as far as I know, Tange Prestige is nothing more than Tange's version of generic cro-moly, the 'Prestige' means it's just been heat-treated for extra strength.