Has anyone tested the difference between Mozilla's Firefox build and a local fully-optimized for your machine build? Or something similar with another piece of open source software. I wonder how much the "Gentoo-model" of compiling everything yourself affects everyday performance.
Everything on my Gentoo system runs faster than in the binary ebuild equivalent.
That being said, things like choosing the wrong preemption mode can introduce latency problems, etc. Most users experience higher throughput and higher latency when comparing Windows to Gentoo. I believe the higher user interface latency is the general case when going from Windows to Linux.