> If it's an optimizatio, can I see some benchmarks numbers? :-)

First create two files. Run unpatched Python:

./python -c "import pickle, lzma; data = [bytes([i])*2**16 for i in 
range(256)]; with open('test.pickle4', 'wb'): pickle.dump(data, f, 4)"

Then run the same with patched Python for 'test.pickle4opt'.

Now benchmark loading.

$ ./python -m timeit "import pickle;"  "with open('test.pickle4', 'rb', 
buffering=0) as f: pickle.load(f)"
10 loops, best of 3: 52.9 msec per loop

$ ./python -m timeit "import pickle;"  "with open('test.pickle4opt', 'rb', 
buffering=0) as f: pickle.load(f)"
10 loops, best of 3: 48.9 msec per loop

The difference is about 5%. On faster computers with slower files (sockets?) it 
should be larger.