I’d assume that anything “traditional” won’t have been touched at all, and anything “new” (like DNN, G-API, …) might have received improvements, but not have regressed in quality or execution speed.
I don’t have numbers though.
OpenCV comes with some performance tests, if you build them yourself. you could run those.
perhaps these tests are also run by OpenCV’s own CI/CD and maybe the results (log files) can be found somewhere.