One other thing I wanted to note is how telling the first page of chapter 515 actually is:
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Its a simple process to work out the size:
1. The intel extractor and the other guy (idk who that is honestly) are seen on one of the turtle's spikes, so we know the relative size of the spikes.
2. The spikes are shown in close proximity to the turtle's head in two separate shots, giving us an idea of how the spikes compare in size to, say, the turtle's eye or pupil.
3. Based on these relative sizes, I'd say a person is about half the size of the turtle's pupil which can barely be made out in the larger image. Bottom line, I'd say that we would barely be able to make out Oonoki and co. under the turtle even if they were in view.
That basically leads to the conclusion, for me, that the meteor is not any bigger than the turtle. I think I can safely say that the meteor is either equal in size to the turtle, or smaller. In reality, I'd assume its quite a bit smaller.