This is a post I did last April. Search oneilkeys and doghouse and you can read the whole series of posts on this issue.
"Took my Vegas on a 400 mile trip from Key Largo to Gainesville FL today and had s chance to test the noise level. At 55 mph I read 78-80 db and at 65 mph 81-82 db.
Even at 65 the engine noise has all but disappeared. Wind noise is all we hear. An added benefit to all the insulation I put in the engine is the fact that at 85-90 degrees on the turnpike, the A/C kept up with the heat and worked much better than last summer. You can feel the difference on the dog house. After 3 hours of driving it was warm, but not hot. I also added an additional layer of tint to the upper windows above the driver and passenger seats and that helped with the heat."