I created a Github issue to address the upgrade to 3.2.13, and pfalls is working on getting this done.
https://github.com/TechEmpower/FrameworkBenchmarks/issues/24...
I encourage you to benchmark Rails 4 yourself and see if there is a measurable difference from the latest 3.2.x, to get a preview of the impact it will have. When Rails 4 is released we'll definitely want to upgrade to that.
Edit: pfalls is too fast for me, and just completed the upgrade to 3.2.13 and closed the issue. The next round will use Rails 3.2.13.