The speedup is impressive. Thanks for doing that. It makes the results much more pleasant to use.

I'd like to suggest two typographic improvements:

It would be nice for Scheme code to be formatted in a fixed-width font. Even better, it would be great if you could use a formatter that supports Scheme, so that keywords would be in bold face, etc.
I found a few instances of raw TeX formatting, e.g. "$\Sigma$" appears in the documentation of string-upcase. It would be good to fix those.

I'm looking forward to everything in your TODO list — and, of course, to SRFI support. Thanks again for doing this.