> particularly as Guile e.g. greatly lags Racket performance

Huh. This has not been my experience, rather the other way around.

I do see a whole heap of benchmarks that contradict it, so I probably should put in some effort to find out why, or if I'm just plain wrong... But at a guess? Guile doesn't have Racket's startup time penalty, and most of what I do is IO bound - and Guile's IO story is better than Racket's.