I do think that , generally, (though i know there are exceptions and that schools dont always get it right ) that pupils given mid L4 grades in maths and english would really struggle with the demands of the 11+ for KE.
As the parent of a boy who had predicted 4s [edit - and that was in Y6
], I think you have to look at a broader picture than that. From the parents we talked to at induction (a tiny and possibly very unrepresentative handful I must admit!) I don't think it's by any means unknown for boys with predicted (or even actual) L4s to pass. You know your own child best and have to make your own judgements as to whether the levels are a (a) a realistic reflection of a child's ability or (b) understate their ability because they're lazy, awkward or uncooperative and don't really operate well in the classroom environment (particularly with boys) or (c) overstate their ability because they conform, work hard and fit in.
[edit again - ews147, it's wonderful to hear that your son passed for KE - I was worrying about you on results day!]