> I would expect the -O2 numbers to reflect better the actual ISA capabilities.

I will have a more thorough look at -O2 too, good point.

However w.r.t. "ISA capabilities" the simple fact is that compilers don't use CISC style instructions. They prefer RISC style load/store + many GPRs code, and new x86_64 instructions are modelled after this paradigm. Hence I wouldn't expect there to be a huge difference at -O2 (and in my experience x86_64 often loses at -O2 too).