IronPython outperforms CPython when not mutating class attributes

IronPython hammers CPython when not mutating class attributes - more information about the performance issue. Here related to IronPython - apparently class variables can be problematic in some cases, as the classes themselves change through them and thus JIT compiler information must be discarded (due to the rather static structure of the VM, both in the JVM and in the CLI, probably a very similar problem), which means the JIT compiler then has to rework everything and thus not only are performance advantages lost, but they can potentially even be counterproductive.