Two runs with standard locks:

D:\pydev\hg\cpython2>pcbuild\amd64\python.exe -m timeit -s "import _thread; l = _thread.allocate_lock()"  l.acquire();l.release()
1000000 loops, best of 3: 0.746 usec per loop

D:\pydev\hg\cpython2>pcbuild\amd64\python.exe -m timeit -s "import _thread; l = _thread.allocate_lock()"  l.acquire();l.release()
1000000 loops, best of 3: 0.749 usec per loop

Two runs with CV locks (emulated)

D:\pydev\hg\cpython2>pcbuild\amd64\python.exe -m timeit -s "import _thread; l = _thread.allocate_lock()"  l.acquire();l.release()
1000000 loops, best of 3: 0.278 usec per loop

D:\pydev\hg\cpython2>pcbuild\amd64\python.exe -m timeit -s "import _thread; l = _thread.allocate_lock()"  l.acquire();l.release()
1000000 loops, best of 3: 0.279 usec per loop

Two runs with CV locks targeted for Vista:

D:\pydev\hg\cpython2>pcbuild\amd64\python.exe -m timeit -s "import _thread; l = _thread.allocate_lock()"  l.acquire();l.release()
1000000 loops, best of 3: 0.272 usec per loop

D:\pydev\hg\cpython2>pcbuild\amd64\python.exe -m timeit -s "import _thread; l = _thread.allocate_lock()"  l.acquire();l.release()
1000000 loops, best of 3: 0.272 usec per loop


You can see the big win from not doing kernel switches all the time. shedding 60% of the time.
Once in user space, moving from CriticalSection objects to SRWLock objects is less beneficial, being overshadowed by Python overhead.  Still, 2% overall is not to be frowned upon.