Most of the time I use 2 models. Mainly because I use a couple of galleries that have sold on tgp so the images are already thumbed and cut to size. Only thing to do is build the 4 pages from scratch. I like using content that has already sold before.
But if I am building everything, pics too, from scratch I will use just one model since I have to grab content its just easier to pick 24 from one group.