From what I've seen Git is very fast compared to Subversion, and I've heard it's somewhat faster than Mercurial, but only by a bit. However, I've not specifically tested it with large, or lots of, binary files.
That being said the way Git tracks changes, I would imagine it's very efficient at dealing with binary files.
I can say this for sure though; Once I got used to Git there's no way I'd choose to go back to Subversion. When I have to work with Subversion repositories I still use Git though git-svn. This way I get all the advantages of distributed version control, but still have really nice support for pushing commits back to the central Subversion repository.
