Seems to me the data for banjo strings are dictated by what's expected:

Assume a 26 inch scale (nut to bridge distance). Tension is whatever is necessary to bring that length of string to pitch, which in the G tuning is G'DBDG with steel strings. Perhaps they would want to plan on the tuning being maybe a whole step or step and a half lower for nylon/gut.

Length of the whole string will be greater than the length of scale, of course, but that's no surprise to a musical instrument string company.

Dave Oesterreich