To add to this, the big thing you get when using Gentoo is to setup your compiler to use all of the optimizations for your exact CPU/other hardware.
The binaries for arch are built for generic x86-64, while your Gentoo system could bet setup to include AMD-specific optimizations or to remove code paths that you would never used based on your hardware.
The result will be that the binaries will typically be smaller and optimized specifically for your hardware.
The downside is that a system update will take you half a day of churning your CPU on compiling.
To add to this, the big thing you get when using Gentoo is to setup your compiler to use all of the optimizations for your exact CPU/other hardware.
The binaries for arch are built for generic x86-64, while your Gentoo system could bet setup to include AMD-specific optimizations or to remove code paths that you would never used based on your hardware.
The result will be that the binaries will typically be smaller and optimized specifically for your hardware.
The downside is that a system update will take you half a day of churning your CPU on compiling.