In my experience, collapsed objects are just (or, should I say, 'at least' as sluggish in 6.1... And, the bounding boxes reflect the missing bits, so maybe it's keeping them in some ghosted form?

Stunning, stunning, stunning, by the way.  I'm very much afraid I won't even be able to look at the clunky little escort cruiser I was working on now that I've seen this.  :-)