Oh, and SRAM doesn't have a 5-speed any more, but the old Spectro P5 is 122 mm OLD for the coaster brake version (and the freewheel version is WIDER, at 123 mm). (The S-RF5(W) you refer to is a Sturmey-Archer product, not SRAM).

I'm leaning towards a vintage Duomatic 102 now for frame reasons - no spreading needed at all. The Duomatic R 2110 would need barely any spreading (2 mm), and the Automatic A 2110 would only need 4 mm of spreading (but it'd still need to be modified - stock, the 28h version shifts at 16 km/h. Better than the 14.9 km/h or whatever it is of the Automatix 28h, but not anywhere near where I want the shift point to be).

Also, with the riding I plan on doing with this bike, I really don't see the point to going past 3 speeds. If I want a wide range, I've got my (X-RF8(W)-equipped) recumbent trike.