python thread scheduler?

[project2501]

i'm doing some benchmarking and python is certainly fast enough (the
time.time resolution is more than good enough).

however, i am using the threading module to implement worker trheads to
hit a server with varying levels of workload.

hwoever, my result graphs (of server response time) are very flat and
these flat graphs are higher with the number of threads. 

this suggests to me that the barrier i'm hitting is the python thread
schedular, not the server software being tested. 

i've verified this with 2 different machines, each runnning the python
client, to hit a server and the graphs are still flat.

any ideas about how i can verify my suspicions and hwo to overcome them?
is there a switch in python that will allow me to have "very independent"
threads? forking takes too much memory and the clients machines get bogged
down beofre the server software under test.