I published some benchmarks of OpenJDK on Mac with Ofast and O3 [1]. Some microbenchmarks like Netty’s HttpObjectEncoder experienced >100% speedup with O3, and the more real-world Dacapo suite was ~15% improvement over O2 (which is exactly the same as Os). I did include a few other flags, however the speedup was primarily due to optimization level.
Building with Os is the old wisdom. It used to be the case that many programs would be faster with the smaller binary size, but this is almost never the case nowadays. - August [1]: http://august.nagro.us/optimized-openjdk.html
