Out of curiosity, why would you go with such a tall mount on a Benelli M4? Unless the scalarworks I saw online weren't the only RMR mounts, but i can't imagine why you'd want to go much taller than the factory irons. Visions of smacked cheek bones due to a poor cheek weld.
As for the question, I'd go with the 9 or smaller. I find the 4 moa dots to be huge personally, have you had the chance to look through any of them?