This week Michael Hudson-Doyle of the #Ubuntu Foundations team published a write-up of our experimentation with the `-O3` GCC flag by default in the distribution.
The tl;dr is that we don't yet believe that the change makes sense globally, but there are certainly come packages that would benefit from using the increased optimisation level.
See the post here: https://discourse.ubuntu.com/t/benchmarking-a-distribution-and-some-o3-results/58027