And since it's a Mac, it is probably llvm-gcc (GCC with an LLVM backend).
A colleague/friend who is developing neural network software recently switched from gcc 4.2.1 to 4.5 (which is still old) and got a 50% speed increase without touching any code.
That's the first thing I thought, too. I'd like to see both Go 1.1 and Go 1.0.3 for a comparison (on this benchmark). I'm hoping that before long we'll be able to count on Go being within a factor of 2 of plain C by most benchmarks.
And I'd like to see CPython 3.3 in addition to PyPy.