I'm not sure if this has been mentioned, but the Taylor Bros. offered the option of a 11/8 top tube on thier lugless solos. I also remember a well known US builder opining that on very small frames a 1" toptube is probably "oversize" and that 7/8" might be more appropriate. Of course wall thickness is a large factor here also. Another intersting point is that while the weight of a tube increases almost in direct proportion to it's diameter, it's torsional stiffness increases as the cube of the diameter and it's deflection decreases as the fourth power ( thanks to Phil Irving).Pretty easy to see how within certain limits the diameter of a tube can be increased, the wall thickness reduced and a resultant structure with reduced weight and similar ride characteristics can be created. I'm sure engineers on the list could explain this better.
Best regards,
Wes Gadd
Unionville, Ct