i didnt get caught, but my speedo was out in my old 32 gtst when i first got it. i realised this the second day i got the car so i was lucky
in my case, my speedo read 15k's over the actual speed of the car so i was lucky :0
so i'd be sitting at 80 on the speedo, but i'd actually be going 65
there's a place in lidcombe called "General Instruments". they can fix the speedo up for you. should cost around $200 in total.
too prove in court that ur speedo was out, u could get them to do a test and give u the results.