EDIT: Workaround. Now we understand the issue, here is the solution: do
git svn fetch -r REVISION:HEAD
where REVISION is t
Try adding the --log-window-size=5000 parameter.
--log-window-size=5000
If the repo has a large number of commits, git-svn will go through them 100 at a time by default. Bumping that up can increase its speed tremendously.
100