So I have two cats, brother and sister and they have been steadily getting bigger. Neither are by any stretch of the imagination overweight (can feel ribs and spine) and they are incredibly fluffy but he is 5.5kg and she is about 5kg (although this may be all fluff).
They are mongrels (if that is a thing in cats) but they must have something in them that comes from colder climes.
Would love to know.