In my experience arm clang compiler often times produced code that is ~10-20 percent faster (hence less energy consuming) than gcc with the same optimisation levels
(Building bare metal code with a lot of DSP and MATMUL)
Yes, especially SIMD Neon where gcc producing horrible Neon code for all versions < gcc-12 even by using simd intrinsics. From version 12 gcc is at same level as clang.
You can try it : https://github.com/powturbo/Turbo-Base64