well if it slows down when you pan around the sceen thin its lickly the video car. If its slow when you pull verts around thin its probably a ram prob.. expecaly if it only happence once you get a lot of polys in there..

if your not always useing the image plan's for ref.. you can speed things up buy terning them off. make a hot key for it if you want. Need help with that just let me know.