Hi Shaun, i just made some calculations simply considering the "working range" of gut strings: Assuming a theorbo in A at a'=440 with first and second course an octave down you would need a string length around 80 cm for the 6th course. The upper limit would be around 90 cm (because of the third course). When you also only want to use gut strings in the bases, the extensions should be around 160 cm.
However, the lowest frequency on which a gut string can be used for a givven string length depends on the instrument and personal taste. Hope this helps, Benjamin (who choosed 7+7, 82/165) To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
