More experiments with star trails
43 minute exposure, f/13 ISO 100, camera noise reduction on. The lower ISO definitely helps with image noise, but combined with light pollution from city lights and the rising full moon, most of the fainter stars are lost.
20 minute exposure, f/13, ISO 100 camera noise reduction off. The bright streak at the bottom is Jupiter. Lots more noise without the camera noise reduction, but you get the image in half the time and get a more shooting time out of your battery.
It's going to be really hard to get good star trail photos in the middle of the city anyway, but it seems like something between f/7.1 - f/11 and ISO 400 gets me some pretty nice shots with my camera.