My recommendation for benchmarking SETI is to set up a new email/seti account and only have the test rig using it, thus providing you with an average WU time just for that machine. That way it will get proper seti work units (as most people get), and when its finished you can always retire the account into your own normal SETI one.
As said before, the D.net RC5/OGR client has inbuilt benchmarking abilities.