Here is a sample of one I did . . .
http://www.PhotoShare.co.nz/PhotoSha...ered4328_S.jpg
The exif info is in the shot. I think it was 30 secs at ISO 400. This was shot RAW and I used 2nd frame noise subtraction (NR). The only reason for using ISO 400 and not 100 is that the light moves around. I also shot some at ISO 200 and 45 secs.
Next time I will probably use ISO 100 and 60 secs or more just to help keep the noise down in the darkest parts.
The thing is it doesn't matter what brand of camera you use for this type of shooting. A faster lens or higher clean ISO might help if you need a much faster shutter speed. Otherwise you could use any decent camera and get great results. The NR (frame subtraction) is a big help for "hot" pixels.
BTW, for film shots it might be worse. Film has something called reciprocity failure, and in the old days you would "gas" it to get high ISO and and reduce the reciprocity failure on long exposures.
Just remember to have fun !!!