First, memory-beta concerns the Star Trek novels, none of which are canon. All information on Borg cubes that came from a novel is also not canon.
Second, memory-beta claims that a baby "tactical" cube is 3,040 metres. You yourself posted a link to a image of Voyager (132 metres max width) adjacent to a baby cube. How can you reconcile the 3,040 metre figure, with the linked image?
Star Trek Online is a internet fansite, they can make up anything they want to play their little wargames. It's all fan fiction, some of it is interesting, but non-canon.