Here is one, simple comparison between 3 different builtin_sum's, all 
measured on the same machine, MacOS X 10.4.11 (Intel Duo):

1) Python 2.5.1 ActiveState with standard Slow Summation:

% python2.5.1 -mtimeit --setup="x=[1.0e12, 7]*1000000" "sum(x)"
10 loops, best of 3: 177 msec per loop


2) Python 2.6a2 (built from source) with the existing Fast Summation:

% python2.6a2 -mtimeit --setup="x=[1.0e12, 7]*1000000" "sum(x)"
10 loops, best of 3: 52.5 msec per loop


3) Python 2.5.2 (built from source) with the submitted Fast Summation:

% python2.5.2 -mtimeit --setup="x=[1.0e12, 7]*1000000" "sum(x)"
10 loops, best of 3: 48.2 msec per loop