I usually go 200 or 400. I could just do 100 and do longer exposures but I like a high ƒ-stop (22 for those above photos), I take bracketed shots, and I don't like having to wait forever for a photo to take.
So basically I often shoot 400 just for ease, or 1600 if I /want/ the grain such as for something like this[url].
Nice shots. I have been experimenting a lot with my new Nikon D3100 DSLR and it is awesome and gives me great shots of my figures. Can I ask how you do the light effects in that one pic? I have seen that before in other pics and someone referred to it as light pen drawing or something like that?