In the arbitrary collection of programs in https://benchmarksgame-team.pages.debian.net/benchmarksgame/... , SBCL runs x5 slower than C, Racket x15 slower than C. Chez Scheme shoud be in between, like x10 slower than C. (Anyway, some C programs use very advanced low level tricks, so the difference with realistic programs may be slower.)

It's a pity they don't rune benchmarks for Clojure, and I have no idea to make up a number.