When you get P5, you get nearly all of the features of ProPack (I believe the only things you don't get are the Hi end app export plugins). Plus the material room (which as others have said is very underrated and underutilized at the moment), dynamic cloth (based on the Stitch plugin for Max), which, while adding draping and rendering time to animations, also lets you avoid many of the problems that conforming clothing can have...and it is also just now being delved into by many. The dynamic hair is also a high end plugin that was integrated (can't think of which one ATM), has a few collision issues, but is starting to show its promise as people experiment, and find out what it can really do. The library enhancements, and the ability to create multiple runtimes to link to P5 are worth it in and of themselves. Then you have the integrated Python scripting; a couple of apps like Metaform exist, and then there are the scripts that Ockham and others have written, that automate or expand Poser functionality. Poser itself does lack goodies like network rendering and several types of lights. However, Bryce 5, Vue4 and VuePro with Mover 5, Carrara Studio, Shade Pro, do have it in some form, as well as more flexible lighting and the ability to import most of P5's content animated (with Vue and VuePro, as long as you have the Mover 5 add-on you can fully import Poser animations with dynamics; the only thing it doesn't recognize is most of the shader nodes; and that may be changing. I -think- that Carrara also recognizes all the goodies in a P5 pz3, but I'm not sure). P5 is the way to go. And as there is no known timetable on P6, you would probably be better off getting P5, learning it, and then taking advantage of the reduced upgrade price when P6 comes out.