You can use trial accounts, which are free.
Sure they cannot go beyond 10th or 20th, and have a bunch of restrictions on them.
But purely as a stress test in Org/SW... should serve their purpose.

With IS Boxer you can run dynamic settings macros.
Have the current window run Settings High.
And the slaves, Window All Without Current run Settings Low.
Make a mapped key for each.
And add two Do Mapped Key actions to your swap mapped key.

http://www.dual-boxing.com/showthread.php?t=32654

That way, the slaves have the least drain on system resources.
And the master/main/active window has the prettiest graphics/effects that your system can handle at a FPS level you're happy with.