The "universal compiler" mentioned in the comments to generate Python from Gambit Scheme source code is amazing. I've used it to interface with Python libraries and it's quite seamless.

Also the Sapphire theme - that's a blast from the past.

That's really interesting. Can you point me at any documentation on using this? The docs don't seem to mention the universal backend, though I see mentions of it in the git logs.

Has anybody had experience with both Racket and Squeak that can compare and contrast them for doing things like this article describes?

I do like Squeak and Pharo Smalltalk implementations, but they would benchmark out quite a bit slower for numerical computations. For reference, look at the programming language shootout benchmarks.