Sorry to barge into this forum but I just wanted to say that maths and English are not intelligence tests because what marks you gain in these purely goes to show what previous education you have received. So, the more able you are generally and the better the primary/prep school you attended, the better you are likely to be able to perform in these tests.
VR and non VR are different. Although practice does make for higher marks some considerable research has been done by the Foundation for Educational Research in this country, which says that the mark obtainable by an individual child can only be enhanced by so much by practice (can't remember what the figures were). Basically, if a child's natural highest ability threshold for an intelligence test is at 80%, then you are extremely unlikely to get that child to produce a result above that level.
The thing with the 11+ and independent entrance exams, of course, is that a considerable number, and I suggest the vast majority) of pupils being prepared are actually reasonably bright so their natural thresholds are high.
Going back to the English and maths, if you have a child in a good preparatory school, where there are, purely for example, 15 in a class, and that child has a reasonable natural ability with maths, then this ability, coupled with the advantage of more of the teacher's time, is likely to result in more maths knowledge than a child in a state school class of 30 with a similar ability.
It is the case, that children from preparatory schools often perform better in entrance exams than their state school peers and this is probably due to the extra assistance/learning of maths and English. As far as the VR and NVR are concerned, these children may still perform better on average. I would suggest that this is because they may be inherantly brighter (their parents hold down jobs which have salaries to pay those school fees and thus had a good education/ability themselves in most cases).
It is my opinion and experience that the main advantage of private primaries is in English (ability to speak, write, read, etc, etc). In this particular area, I believe privately educated 11 year olds have a huge advantage over their state school peers.
I would have used the private system for that very reason, if I had had the money.
Good luck with the exam/s