@mischievoustomato >do you customize build stuff on gentoo?
That's quite a broad question, I enabled / disabled some useflags based on personal preference and compile with -march=native and -O2. As for patches those are rare, the only one I think I still have on my desktop is a Qt patch that fixes compiling on -march=native for my CPU. Most of the time my patches are for musl crap, on the systems that have musl libc.
Kernel is whatever gentoo-sources has available at the time, also coompiled with -march=native.
Oh and I have some special env files for portage that compile certain packages with clang or clang-lto, all personal picks that I wanted to try clang or LTO on.