I'm also battling road noise, so let me add what I know:

I tore out my interior and put butyl mat on the floor, back seats and doors, it was a big project, and it didn't really reduce noise. Maybe the doors did a little. I still wear earplugs on long freeway drives.

Then I started reading write-ups on www.DIYmobileaudio.com, and I learned a lot. Foam is what blocks or absorbs noise, not mat. Mat reduces panel vibration. Open-cell foam absorbs noise, closed-cell foam blocks it. The thicker the foam, the lower frequency sound it is capable of stopping.

Raam Audio (www.raamaudio.com) makes a product called Ensolite specifically for noise reduction. I'm finally ordering mine tonight. Raamaudio (Rick) is a member of diymobileaudio.com and is building up a project Scion tC for autox and sound quality competition, and it's coming out lighter than stock with a system in it. You can read about how to efficiently reduce noise on that site. It also involves egg carton-shaped foam where there is more room, like inside your doors. Apparently this can also make your door speakers sound smoother by softening the surface behind them.

-Dan

P.S. If you put all this work into your car and turbo it, I hope you will keep it for more than 5-6 years!