I went 5 low-B in the mid-1980s, and moved to the Steinie 5 in '90. 18s on the bottom, 2x8 + a titanium horn up top, biamped with a GK RB-800. Once I played it, the "why a five" question stopped. 13.5mm string spacing.
I managed to get a mid-generation TL-Six custom (after 1st gen, before 2nd)...