[plt-scheme] efficiency

I'm trying to compile a program with mzc, and the result is about 5x
slower than the same program complied with bigloo. That is, the bigloo
version finishes in about 1 second, the mzc in about 5.

Perhaps I'm doing something wrong that someone can clarify. First I
added the appropriate include to my file (which has no module
declarations or anything like that):

        (require (lib "pregexp.ss"))

Then I compiled:

        mzc --unsafe-disable-interrupts --unsafe-skip-tests \
            --unsafe-fixnum-arithmetic --prim plt-foment.scm

Then I created this bootstrap script:

        #!/bin/sh
        mzscheme -evm '(load-extension "plt-foment.so")' -C

That's it. For the curious, the bigloo went:

       bigloo -Obench -unsafeatrsvl -hygien -farithmetic -Wall -copt \
              -O3 -o foment foment.scm

While I'm on the subject, I wonder why there's no "mzscheme runtime"
-- why mzc requires the mzscheme executable and can't just link the
native code to a library.

adrian