How does the size of a Borg Cube compare with the size of the Crystalline Entity? With the size of Deep Space 9? How does the size of Deep Space 9 compare with the size of the Crystalline Entity?
I don't know about the Crystalline Entity, but this site has comparisons of the various ship sizes, as well as comparisons to other universe ships.
Also, you might like this: http://www.ex-astris-scientia.org/fleet-charts.htm Again, no Crystiline Entity
It doesn't really matter now how big the crystalline entity was, because it was destroyed by someone with good sense, Kila Marr. Not that Jean-Luc Picard would know anything about that.