I think 39 MPH OVER the speed limit is going to be frowned upon in just about any jurisdiction, so any doubt that you can cast on the accuracy of the measurement will help you. In some states, anything over 20 above is considered reckless driving (e.g. WV).

In my non-expert opinion (most of my experience has been in Maryland... about 12-13 tickets in 17 years of driving) you don't have a strong enough case to take it to trial without a lawyer. If you're pretty articulate and don't intimidate easily you probably have a 50/50 chance, depending on the mood of the prosecutor, judge and jury (if applicable), but you've got to decide whether it's worth the risk of paying the full fine and points should you be found guilty. If it were me, and I was convinced that I was without a doubt doing less than 90, I would most certainly take it to trial. But that's me, and I've been to court enough to know how to present myself and what to expect.

If you don't have a lot of personal experience in the courtroom, you're probably better off hoping for a break or a plea bargain. Go to court; look for the cop; if he's not there, plead innocent and be on your way (there's your break). Otherwise, plead guilty and ask for a reduced charge.

One thing you should be clear on is whether your insurance company uses points to determine your rates. MINE (USAA) DOES NOT. Mine uses your conviction against its own point system, so regardless of whether your DRIVING RECORD has 0 points or 10 points, your rates do not change. Driving record points only come into play when they decide whether to suspend or revoke your driver's license. My insurance rates fluctuate based on number and type of convictions and accidents during a 3 year window. So in my case, I'm more concerned with the conviction (i.e. 0-9 over, 10-19 over, etc.).