Peter advized me to make some changes to the cable routing, so now the shift cable goes over the main hinge on the left (as before) and then goes over the top of both chainstays and on the outside right of the chain into the rear triangle and the hub attachment. Maybe kind of hard to explain, but I can take a picture if someone's really interested. The old routing had the cable going over the main hinge, then under the chainstays and inside the rear triangle to the hub. The new routing definitely has less sharp curves in it, but I had expected the effects on the shifting to be minimal. Actually, it was quite noticable. When upshifting (especially from 3 -> 4) there used to be a delay, but that has pretty much gone. Presumably that was due to friction where the cable was sharply bent before.

I've also been thinking about Wav's comments on the Sturmey shifter. I must admit that when I first unpacked the shifter it seemed very plasticky and cheap. However, it feels much more solid when installed and I quite like the shift feel and action. I felt the Nexus shifter on a bike in my local bikeshop the other day, and it felt very stiff by comparison (that could just be the way they set it up?) but I didn't ride the bike so don't know what it would be like in real use. I guess shifters are very much a personal thing.