SRAM DD - 540%
Sturmey-Archer CS-RF3 - 516%
Back when this hub was introduced (2012 or there abouts) this question was asked on multiple forums. A Sturmey-Archer company guy named David Prosser said one could use a primary input drive ratio on the CS-RF3 of 22x34 (i.e. 0.65 to 1). Mr. Prosser said the hub had been tested to 780kgf-cm,
the maximum tensile strength of the chain used in the tests.
Derailleur clearance with 16" wheels? Shucks, use the smallest rear derailleur made:
great info! Seems like the hub is pretty much bomb proof