On Mar 6, 3:26 am, (Henry Spencer) wrote:

Interestingly enough, both the Titan II first stage and the S-IC had lower
tank mass, in proportion to contents, than the Atlas E did. (Some of the
other Atlas variants may have done better, but I don't have numbers for
them handy. Atlas tank-wall thickness got dialed up and down to suit the
application.) Mind you, the Titan stage benefitted from higher propellant
densities, and the S-IC from sheer scale.

There was a proposed S-IC stage and a half derivative, the S-ID. It
would drop the 4 outer engines (to be recovered) and was capable of
orbiting 22 tons.
I wonder if it would have had a lower cost than 2 stage EELVs.
The up side was retaining heavy lift capacity.
http://www.astronautix.com/lvs/saturnvb.htm