I just upgraded after using 4 for several years, and am very happy with 5 - if for the filing & organization system if nothing else. My poser collection has outgrown 4's rather basic organization structure. The morph control is better, and the new version seems to run as well as 4 (knock on wood). Also the render engine, even using the Poser 4 engine at quick speed, is better to my eyes than the render in 4.