I have the same trouble in P5 with many characters in a scene, it slows to a crawl and sometimes quits completely. P4/PP handles these same scenes with ease. I guess with P5 you're just stuck making smaller scenes. I, too, noticed changes in my P4 setup after installing P5 but I don't remember exactly what they were. However, they were nowhere near as bad as the problem you have. I woulnd't now how to fix it, sorry. Good luck.