Yeh Beaker, I think the cross/stake argument is not impressive to devout JWs. It's not really something that matters much. It will put them off listening further.
I've found if you stick to prophetic interpretation when talking to JWs - eg tell them why you no longer believe in 1914 (read Carl Olof Johnson's book and ewatchman's reasonings on it), that is more acceptable to them than doctrinal arguments, because JWs know and accept that the WTS stuffs up on prophecy. Then, when they've got questions buzzing in their heads that have to be answered, they may start looking deeper into the 'truth'.
moogs