It does not matter with how good a compiler you compile an interpreter it stays an interpreter. With Pypy you get a JIT Compiler. Sure you could maybe write a JIT with CL but thats a lot more work.
CLOS implementations have had to deal with the problem of extreme dynamism for a long time, so there has been quite a bit of optimization work associated with it. Polymorphic inline caches help a lot, for example.
That said, a good tracing JIT is probably better; but on the other hand, SBCL has profited from many years of optimization work on CMU CL. It would be interesting to see some real-world performance comparisons between SBCL and PyPy.
Wouldn't SBCLs type inference(+ type hints) help with this? I'm no compiler expert, but i think clojure(with the possible exception of multimethods, which are slow even on the JVM) would map well to CL(maybe even better than the JVM).
PyPy is not just an Python-Interpreter. The PyPy Team build a Toolchain that can creat a JIT-Compiler out of a Interpreter (read some about the pypy project and you will be enlightened. Such a Toolchain does not exist for Common Lisp.
