Recently, I've been struggling with performance in Git Bash on Windows. Just doing a 'git status' takes several seconds.
Directory browsing was also crazy slow, just TAB completing possible filenames was taking a few seconds.
After doing a bit of Googling, I found a few tips that made a huge difference to my experience.
Make the following changes to you git config:
Another speedup came when I redefined my shell prompt. By default, the bash shows you which branch you're currently on, and for some reason the method it uses to get the branch is quite slow.
I found the following change on a StackOverflow post that seems to work way faster:
Make sure the PS1 variable is not changed again later in the script.
These tips all came from a StackOverflow post: http://stackoverflow.com/questions/4485059/git-bash-is-extremely-slow-in-windows-7-x64, there may be more there to help, but just the above changes made a massive change for me.