I found the following quote from http://c2.com/cgi/wiki?SchemeImplementations helpful:
performance: Depends on what you're doing, but in general, -C compilers (Stalin, Bigloo, Gambit, Chicken) come at the top, with Stalin somewhat faster than the others; some compilers (mzc) are on par with fastest interpreters. Interpreters fall in three classes, fast (Racket, Gauche, RScheme, STklos), intermediate (Scheme48, scsh, SCM, MIT Scheme, Guile 2.0) and rather slow (guile1.6). guile1.4 is yet slower.
- (Added 2017-08-22) Recent results from a benchmark for R7RS implementations.
- an opinionated guide to scheme implementations by Andy Wingo.
- Scheme Unicode support comparison.