I also have a Shoei RF-1000, and an HJC AC-12. While the AC-12 is quieter, I think the point is moot with helmets, as they all have resonant cavities that will do what the do naturally when air flows through them. If you look at helmet reviews over at
http://www.motorcyclegearreview.com you'll see all helmets have noise complaints.
I'm not sure how effective the Windjammer is, it may be the kind of product that may work better with some head shapes than others, which incidentally is also a criteria that will determine how much noise will be generated within a given helmet. An RF-1000 may be whisper-quiet on one head and roaring on another. The general consensus is that it's noisy.
In the winter I essentially seal that neck area up in a manner similar (if not more so) to what the Windjammer would do, and I would still wear earplugs.
I don't ride with the Shoei anymore because it's tendency to fog almost had me killed once. The AC-12 comes with an anti-fog coating right from the factory.
But that's a different topic...