I see in DM-SG0005-00-ENG, page 6, that Shimano recommends a primary drive ratio between 2.3 to 2.6 for the Nexus 3-speed hub.
Several folks told me that Sturmey-Archer recommends a primary drive ratio of no lower than 2 for the AW family of hubs. Despite swearing on an original copy of Harold Briercliffe's Cycling Touring Guides - Scottish Highlands that 2::1 is gospel, no one has yet been able to reference this in S-A's modern or historical literature for me. Anyone?
I run 42/22 on both the WWII-era AW and the SRF3, and 36/19 on the "don't post that @#&*$% on this forum" S-A three-speed.