As noted in a posting to python-dev, I've re-evaluated my test methodology.
The results are as follows, with details of the PyBench runs in the 
pybench_summary.txt attachment:

----------------------------------------------------------------------
test        trunk                no-freelists         LIFO(500i,100f)
            case 1    case 2     case 1    case 2     case 1   case 2
----------------------------------------------------------------------
pystone     26500     26100      27000     25600      27000    26600
int 1       7.27us    9.09us     6.69us    20.4us     6.64us   9.25us
int 2       10.4us    9.48us     20.9us    20.9us     10.5us   9.69us
int 3       381us     360us      792us     813us      805us    780us
int 4       393us     373us      829us     834us      844us    799us
float 1     1.14ms    1.1ms      1.2ms     1.2ms      1.2ms    1.27ms
float 2     773us     831us      1.05ms    908us      865us    967us
float 3     733us     759us      970us     825us      804us    906us
float 4     74.6us    76.9us     100us     83.7us     77.6us   86.9us
float 5     7.88ms    8.09ms     10.7ms    8.93ms     8.46ms   9.43ms
pybench     16716ms   16666ms    16674ms   16612ms    16612ms  16611ms
script a    30.7s     30.6s      33.0s     33.0s      32.3s    32.6s
script b    41.7s     40.6s      42.1s     39.4s      40.5s    41.8s
----------------------------------------------------------------------
case: 1=std, 2=no small ints


test details
============

pystone:
 average of 3 runs

int 1:
 ./python -m timeit -s "range(1000)" "range(250)"

int 2:
 ./python -m timeit -s "range(1000)" "range(257,507)"

int 3:
 ./python -m timeit -s "range(10000)" "range(10000)"

int 4:
 ./python -m timeit -s "range(11000)" "range(257,10507)"

float 1:
 ./python -m timeit -s "[float(x) for x in range(1000)]" \
 "[float(x) for x in range(1000)]"

float 2:
 ./python -m timeit -s "map(float, range(1000))" "map(float, range(1000))"

float 3:
 ./python -m timeit -s "t = range(1000)" "map(float, t)"

float 4:
 ./python -m timeit -s "t = range(100)" "map(float, t)"

float 5:
 ./python -m timeit -s "t = range(10000)" "map(float, t)"

pybench:
 average runtime per round of ./python Tools/pybench/pybench.py -f <logfile>

script a:
<code>
import time

def b(time_now=time.clock):
    limit_val = 2000000
    d = [None] * limit_val
    start_time = time_now()
    for j in xrange(25):
        for i in xrange(limit_val):
            d[i] = i
        for i in d:
            d[i] = None
    return time_now() - start_time

if __name__ == '__main__':
    print 'elapsed: %s s' % b()
</code>

script b:
<code>
import time

def b(time_now=time.clock):
    limit_val = 1000000
    f = [None] * limit_val
    d = range(limit_val)
    start_time = time_now()
    for j in xrange(25):
        for i in d:
            f[i] = float(i)
        for i in d:
            f[i] = None
    return time_now() - start_time

if __name__ == '__main__':
    print 'elapsed: %s s' % b()
</code>