Here is an updated patch for both multi-methods and RestFn.
I have also pushed a project to http://github.com/pjstadig/blow-heap that has some (gratuitous but automatically generated) tests for every arity combination.
There is a bin directory in that project that contains a blow-heap.sh file that can be run. It will call out to leiningen to run the tests, and the project.clj file is configured to start Java with a sufficiently small heap.
You can change the dependencies in the project.clj file to clojure 1.2.0, run the script, and see it fail. Then apply the patch to clojure, `mvn clean install`, go back to the blow-heap project and change the project.clj to use clojure 1.3.0 SNAPSHOT, `lein deps`, and rerun the tests to verify. (Whew!)
I believe this patch should also apply cleanly to the 1.2.0 branch, since the multi-method and rest-fn classes haven't changed since then, but if that's not the case I can send another rebased patch.