There is no point in putting your child through unnecessary extra exam testing as if your child is capable of passing the 11+ he will be accepted by the grammar school you choose to place first on your preference form.
Select the grammar school you all feel is the right choice and apply to that one alone as your first choice secondary school on the preference form. Grammars admit the top achieving 120 - or 150 in the case of TGSB.
We have just been through this "harrowing" process ourselves and we considered the same question. I have researched this whole topic thoroughly and spoken to/emailed/telephoned LEAs and grammar schools.
My daughter passed and starts at her chosen grammar in a few days' time.
The big problem with applying to the Devon or Torbay grammars is that if your child is not in the accepted cohort, your second choice/only remaining option in the state sector is a comprehensive. Otherwise it means private!!!
Hope this is useful. Best of Luck in choosing!