This performance gains myth sounds like exactly the same wishful thinking as we used to heard back when Gentoo Linux was The Cool Hotness(tm). Don't get me wrong, Gentoo was great, but its added value was not in the compiler optimizations, but rather in the modularity, where you could select a feature set you wanted for your system, and not worry about useless dependencies, their associated support libraries and bugs or vulnerabilities in those.

And when it comes to the kernel, can compile your own on any distribution, including using or omitting any kernel patches you want.