From my own experiences and what others have posted around here using a second GPU to render WoW only hinders performance. The only real reason to use 2 [or more] GPUs in a single system is to run more monitors. If WoW isn't launched from the 'primary' video card then it's rendered by software and not your video card's hardware [correct me if I'm wrong]. Also with SLi or Crossfire WoW gets no advantage from it what-so-ever...it could even hurt performance.