Matt, A similar thing happenned to me (73 in a 55) and I challenged it.
I sat in the lobby with the police officer who gave me the ticket prior to the hearing and he was really helpfull. He practically told me what to say - "That I don't believe I was doing 73 mph and that I would like the officer to inform the court when the last time his gun was calibrated and what the margin of error is."
I argued that "based up the margin of error of 5% I was under 70 mph and the fine and points are too high"
I didnt get the ticket thrown out, but the magistrate did remove a point and a few dollars from the original ticket.
You have nothing to lose - You pay court costs whether you challenge it or not.