Malcolm, the ISS pass shot is quite good as it looks like something large compared to background stars.
I have been starting out on piggyback as my planetary and deep space is still very limited. I found the only way to keep noise down is use ISO400 if possible which means someform of piggyback on a tracking mount.
I don't really have much of an appreciation of suburban skies as I am in the country down here and light pollution (esp out of town) is minimal so I can go out to 3 or 4 minutes.
Maybe try piggyback with ISO400 or 800 at most and I found my 40D performs really well below 5 degC and noticeable worse above 15 deg C with this latest round of warm spring WA weather we're having.
Darrin...