I don't like drywall that close to the Durarock. If necessary, we put a water proof membrane (always 2 layers behind Wonderboard or any wall board, cheap insurance) between drywall and wall board. Often we float our walls. Wall board will soak up water through grout joints, and that water will wick its way to drywall causing all sort of issues.
Here's the top view of what I am talking about.
