I wouldn't dismiss the possibility of using darcs for your project. git was designed to merge tens of thousands of lines of code in a fraction of a second; that doesn't mean it isn't useful for other tasks, but it also doesn't mean that darcs might not be better for the kinds of tasks that you find yourselves needing to do.
Git was also designed to have a fast, simple back end, with a script based front end. Each command that you're used to using with git is just a shell or perl script that calls a few basic git functions to mess with blobs. Therefore, it is easy to add new tools and scripts. A good example given the darcs context would be: http://raphael.slinckx.net/blog/2007-11-03/git-commit-darcs-...
My point is that the architecture of git allows us to write scripts that work at the same level as the other git scripts; we can keep or leave the others as desired.
