I've wondered for a good while if using O2 on stage1 might be worth it. So I did some measurements and it should be worth it for most cases. For a single "quick" flavour build they are more or less on equal footing. If you rebuild stage2 multiple times reusing stage1 it will be faster. If you build stage2 with optimizations/profiling it will be faster. Below are the timings using "time make -j9" for a quick build. I forgot to write down the seconds as I didn't expect them to be so close. But it is what it is. Timings stage1 options O1 vs O2, quick build after make clean: stage1 opt | time (wall) | time (user) -O1 | 13m | 53m -O2 | 13m | 51m I've also run the numbers for a optimized stage2 compiler a while ago, where stage1 with O2 was faster. But I no longer have these numbers around. So it seems safe to say one should use O2 if either: * stage2 is built with optimizations * you freeze stage1 and reuse it while working on stage2