Git's attitude, AFAIK, is that if you want per-file comments, make each file its own checkin. There are pros and cons to this.

Performance as a feature, OTOH, is one of Linus's three tenets of VCS. To quote him, "If you aren't distributed, you're not worth using. If you're not fast, you're not worth using. And if you can't guarantee that the bits I get out are the exact same bits I put in, you're not worth using."