I have been working on an extracurricular project for my day job lately and haven't had much free time for programming. Somehow, a random web search led me to Erlang today, which led me to a description of Termite for Gambit Scheme, and I started looking at some of the other Scheme-to-C compilers. I would have expected Chicken's Cheney-on-the-MTA design and fast first generation garbage collection to give it strong benchmark results, so I was surprised to see Gambit rules. It has a very accessible compiler. It's funny that I have spent enough time working in Scheme lately that I find Gambit's Infix Extension jarring and a little repulsive. Gambit is apparently built and tested on OS X regularly, so I know it is a good match for my G4 PowerBook. What does this page mean by "mangled source file ... is bloody hard to read because of the lack of a macro-expander in gsc."?
Twobit Larceny has a good showing in its own benchmarks, but it is image-based and its primary build is for SPARC. I don't like its FFI either. Gambit is a strong contender on that page, beating Bigloo spectacularly on CPS benchmarks, and ranking a close third overall.
Is PLT Scheme really that good? The MZScheme variant lets you choose between bytecode-with-JIT or a native code runtime.