Here is a small utility written in Python, Pymacs for Emacs while working with Git. While you are viewing a file in Emacs, if you issue a M-x githist-do-show-version it will prompt you for a number, and the script will go back that many numbers back on master branch - it basically runs
git show master~[number]:path/to/file/starting/from/dotgit/File.extand show you the contents of that file in a new buffer. To install the code see here, drop it under site-lisp and change your .emacs as
(pymacs-load "/usr/share/emacs/22.2/site-lisp/githist") (defun githist-do-show-version(num) (interactive "nHow many commits back: ") (githist-show-version num) )