I've imported poser figures into blender 2.42a and used the proportional editor with no problem.  Occasionally it'll get a bit slow, but just for a few moments then it works just fine again.  Thats with 778 RAM.  It might just be that you're using an old version?

Actually, if you plan on getting the figures back into poser afterwards you'll want the new version anyway, the obj exporter is better.  You may still have to manually rename groups in the obj file, though...?