P6 and P7 added some nodes that P5 doesnt have (dont ask me what) . Many materials will work but obviosly any with nodes P5 doesnt have wont work.

Multiple runtimes will cut down the time Poser takes while scanning the runtime , but you get a small delay every time you switch runtimes.

Moving crap you rarely use is a good first start. er. make that , Moving the wonderous but rarely if ever used content :)