Dual 1.8 G5 vs Single 1.8 G5 (purchasing advice)

Hey all,
I am fairly new to the Mac processor world and my company was going to buy a few new machines for some of our art people. They mainly just use Adobe photo and QuarkXpress. They don't do any audio or video editing. Do you think they would need the dual 1.8 G5 or will a single handle the load? Most graphics aren't very intense either. They mainly make graphics for mailing as we do some direct marketing. I think a single could handle their work, but I don't know to much about the mac architecture and was looking for advice from someone that actually uses them for work.

Obviously dual is faster, it depends on the project sizes. If your working on whole bill boards, then go with the dual processor. If your just making letter size prints, you dont really need dual..