So just note that if you go to trial, they will amend the speed up to 81 in a 50 (31 over) as that is what the officers notes say. From demerit perspective, I think 31 over is 4 points and 29 over is 3 points, but demerits have nothing to do with insurance. From an insurance perspective, 29 over and 31 over are both minor and are viewed the same by insurance company, so either one will have the exact same effect on your insurance rates.
Officer notes look execellent with nothing missing. If you testify that there was a car in front of you and officer says there was not, they will usually believe the officer in less you have a second witness that can testify and verify your side of the story.
When did you request a trial? Right away, or did you choose Early Resolution first? The counting of time for a "speedy trial" charter argument does not start until you request a trial. So if you requested trial right away when you got ticket, then it would be over 11 months which would give you a good chance of succeeding with a charter argument.
If you go to trial, you should not testify unless you 100% can say that you were not speeding at all. Speeding is absolute liability so if you get on the stand and say you were only going even 1 km/h over the speed limit then you have admitted to speeding and then with the officer saying you were going 81 they will ding you with the 31 over. So if you were not speeding at all then you can get on the stand and tell what happened. If you were speeding even 1km/h over then do not get on the stand and do not testify and do not give your side of the story.
So besides the possible charter argument above, cross-examination and bringing doubt to officers testimony is the only way to win.
Read these posts:
http://www.ontariohighwaytrafficact.com/topic7039.html -> Representing yourself
http://www.ontariohighwaytrafficact.com/topic7041.html -> Cross-examination
http://www.ontariohighwaytrafficact.com/topic7284.html -> Win speeding trial
http://www.ontariohighwaytrafficact.com/topic7286.html -> Win speeding trial on appeal