It depends on what you plan to be doing. If you'd like to skip the need to use Poser when building scenes, create realistic hair easily, make very realistic outdoor scenes using oceans that animate or do any kind of scene and content creation v.s. simply posing characters, than C6 is a good choice. C5 is a great program though and if you don't plan on using any of the new features that ship with C6, there is no pressing need to update.