The problem is that I also want a fast log/blame for any file back to the beginning of time - but I'm ok with that requiring devs connecting to the server containing the history (as with svn).

I also haven't found a way to make git work smoothly in shallow mode as the default, e.g can I make checkout of a branch always remember it must be shallow? Can I make log use remote history when necessary etc? I don't want to fight the tool all the time because I'm using a nonstandard approach.