Quad Core or Duo Core? I am using iMac i7 Quad core, runs quite smooth. Though occasionally slow in rendering the previews. however, I have to add that I may not be using it efficiently as my library runs into 20k shots. (Juliene Kost kept saying there is no reason to keep multiple library, hence i only use 1 for my entire collection). It wasn't like that. I was migrating my library from iPhoto, and when the library was still small, there wasn't any slow rendering detected. It also did not happen when I was doing the trial.
hope that helped. I do think it will work fine on i5, Quad core nonetheless.