Vague paper submission guidelines - can I use double column if not specified?
I would look at past editions of the conference proceedings to see what style they were ultimately formatted in. Double-column (like IEEE) is typically denser than a single-column, so by picking a two-column format, you may be giving yourself some extra room that other submitters won't have. But you may lose this advantage if your paper is accepted and the format was intended to be single column, since you may have to cut something like 20% out of the content if you are already pushing the limits.