In reading just a little on this subject, I suppose it might make a difference whether a person was using an American malt with its generally higher protein levels, and a Continental malt with lower protein. This is independent of modification of course, but I'd guess that generally higher protein levels would leave more protein even once well-modified.
Well, my first experience with a long p rest was when I was making an Ofest using about 90% Great Western Munich. It was also my first attempt at decoction and the mash sat at 122 for over an hour. The resulting beer had the body of water and wouldn't hold a head no matter how high we carbed it.