Benchmarking The Linux Kernel With An "-O3" Optimized Build
When running various OpenGL and Vulkan games and other graphics test cases, there wasn't any measurable difference from the -O3 kernel build. If -O3 optimizing the user-space Mesa driver components and the game itself is likely a more noticeable impact than from having the kernel -O3 optimized.
Or with ParaView workstation visualization software, no difference out of the -O3 kernel build.