So as to better package gambit in nixpkgs, I tried the benchmarks at https://github.com/ecraven/r7rs-benchmarks with Gambit 4.9.3 on my x64 machine.

Often -O1 was slightly faster than -O2, sometimes the opposite, with the difference usually less than 10% either way, but up to 17% in favor of -O1 and up to 43% in favor of -O2. However, -Os most often beat both -O1 and -O2, so that's what I chose in the end for NixOS.

Note that AFAICT, the benchmark compare the compiled code, not the compilation time. I admit I failed to check the compilation times. I assume -Os is slightly faster than -O2 and somewhat slower than -O1, but would have to check on Gambit-generated code.

PS: I also assume clang is still desperately slower than GCC in the code it produces for Gambit.

—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Those who do not understand Lisp are condemned to not even being able to reinvent it poorly. — Faré, without apologies to Henry Spencer.