What’s the test software / benchmark I should use on Linux nowadays to measure (and compare) shader and raw GPU performance? That would ideally run under both X and Wayland?
I have always tended towards Phoronixs test suite (https://www.phoronix-test-suite.com/) but Im sure there are a few specific to Vulkan around. Not sure about wayland.
The application(s) you want to run is the best benchmark.
Problem with this is that the application I have in mind doesn't provide anything but perceptual feedback. I'd rather have some cold numbers that are to some degree reproducible and would give at least rough idea of the performance of given HW+drivers+other-settings combination.