Here is a simple benchmark (Linux, gcc 4.7.3):

$ ./python -m timeit -s "words=[w for line in open('LICENSE') for w in line.split()]; import collections" "c = collections.Counter(words); c.most_common(10)"

- 64-bit build, before: 313 usec per loop
- 64-bit build, after: 298 usec per loop

- 32-bit build, before: 328 usec per loop
- 32-bit build, before: 329 usec per loop

- x32 build, before: 291 usec per loop
- x32 build, after: 284 usec per loop