I'm getting an Optio S camera as a first camera, but it'll only really be for taking general snaps until I can figure out what all the bells and whistles do. First things first, what sort of resolution should I be using to get good prints for each size. i.e. 4 x 6 should be what resolution? 1600 x 1200? I just don't know, don't want to waste precious space that I don't really need.