I think that is why this blog is particularly interesting to me. As one of the other comments to this posting said, it is nice to see an analysis/detailed description of working to optimize code where the first step is not to rewrite in a language with a presumed better performance baseline. Also, I think there is also some props to be given for continuing to work within Guile's somewhat spartan tooling to do the optimization work, instead of switching to a language that may have more/better tooling for the task.

Not to take away from the general comparisons between various Lisp flavors and between various scripting languages (an activity I engage in quite often), but your lead off line is more prescriptive than I find advisable. I don't think a blanket statement that optimizations of runtime behavior of code "should" only be done via a compiler. Some devs enjoy the work, others have varied reasons for doing performance sensitive work in a given language/environment. But at the end of day, doing optimization is a valid usage of developer effort and time if that developer judges it so.