Interesting to see, though Powerslave and TBoS are slightly skewed by having one song that's significantly longer than the rest. Ancient Mariner is around double the length of its parent album's next longest track, then Empire of the Clouds is five minutes longer than The Red and the Black and eight minutes longer than the title track. I don't think the result would be much different for Powerslave as every track is around 4 - 6 minutes, but I'd be curious to see what TBoS would be without Empire, as I think that's one of the better-balanced reunion albums.