Ya'll didn't really answer the man's question.
Yes, the 06's will be a little power reduced as compared to the U.S. empty catbox 05's, but for California and the rest of the world there isn't any difference as they all have the full catbox.
The real question is if you're gonna notice the reduction. Probably not. The Rocket will still feel **** fast if you're a new owner, so look at it this way... You'll just gain that much more with the before mentioned mods AND really notice the difference.