Your problem is more a matter of wind noise than road noise. In any case, dynamatt will help, but will add weight, and is VERY expensive. There are cheaper alternatives out there that work exactly the same. It's called Rammatt, I believe. I'm sure I'm getting the spelling wrong, but that's what it's called.

Good places to put it are up against the fire wall, in the doors, under the carpet. But that'll only do so much. The majority of high speed noise is from the a-pillar and front windshield edges.