Motor: Crank Drive or Front Hub (because of Nexus preference)?

[flecc]

Finally, one point has just come to mind, and it may or may not be relevant to the problem we experienced with the Nexus not immediately changing gear under load. The bike in question had the “retro-pedalage” or coaster brake option. Could a mal-adjustment of this be a contributory factor in the problem?

I don't see how it could, since it only comes into play when back pedalling. I come from the days long ago when hub gears were dominant and derailleurs a rumour, and in my experience all hub gears have some dislike of changing under load. When the load is motor as well as cyclist and the gear is a very low one, that's likely to be exacerbated by the high torque present then.

As Arstu said earlier, they change best with a pause in the applied load. That said, Shimano's are the best of the bunch, one could die of boredom waiting for an SRAM P5 hub gear to change down.
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[Croxden]

Being in town that meant starting in bottom gear (or reverse gear when exiting my garage) and of course switching off and restarting in gear when traffic lights stopped me.
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Now that takes me back, I also found that changing gear was smoother without using the clutch. Just have to time it right.

I much prefer the automatic I have now.