Are there available benchmarks around how much the performance changes?
It depends a lot on the project and your CPU. Incremental build (build, change 1 thing, rebuild) times are affected more than clean build times, because linking is a larger % of an incremental build.
When I benchmarked it about a year ago (with a fairly large Rust project on a 24-core machine), incremental builds went from ~8s to ~2.7s.