Homebrew git reporting older version

git is installed by Xcode. I doubt you'll have any problems if you replace it, but I can't give you a definitive answer to that…

1. What I'd do is rename the old /usr/bin/git to git_old, then rely on your path to select the new one.
2. If that doesn't work, move the new one to /usr/bin. I doubt Xcode is picky about which version of git it's using.
3. If that still doesn't work, move git_old back to /usr/bin/git and use either a direct path, rename, or alias for your new one.

I doubt you'll have to go past #1 above, though. That should be enough.

Edit: I read your original post backwards. The first thing you should do is make sure your path includes the new git directory BEFORE the directory that contains the old git.

Do you have several versions of Node installed via homebrew? Every time it updates node homebrew puts the newest version alongside the old one and then updates the symlinks to the newest version. Running the brew cleanup should reduce that up a bit for you.