Also i remember reading an article about how big caches and clever precaching on modern CPUs meant that O3 was better than Os now. i think it was a report by intel. but i can't find it.
"native" should be the same as "core 2" for my hardware. I might include LTO last for GCC along with the ICC-specific settings suggested above for ICC. First going to run through the rest of the compilers though... it takes a long time .