Well, firstly, as Rob stated, a speeding ticket of more than 150 km/h does NOT automatically get you a charge of s172. You can be convicted of SPEEDING for any speed.
Now OP. as has been stated, IF you decide to go to trial, (which is YOUR right to do so), you need to be aware of a few things which have been covered, but in many different replies. The crown has three options available to them.
1. Proceed with the 30km/h charge
2. Amend the charge back to the 60 km/h charge
3. Request the court permit the charge to be amended to a s172 charge.
Now, if your found guilty under:
Scenario #1, you will get for insurance purposes a MINOR conviction, and "could" see a 10% hike in your premiums. It really depends upon your insurer some check, some don't some apply the surcharge, some don't.
Scenario #2, you will have a MAJOR conviction registered, and again the consequences will vary by insurer, except NO insurer isn't going to impose the surcharge.
Scenario #3, Again MAJOR conviction, plus you could face a licence suspension, ($150 reinstatement fee). NO insurer will overlook it, and some "may" even drop you, in which case then you must report that you have had insurance cancelled, when shopping for a new policy, (which will mean a significant increase and possibly even mean you have to go to the facility market for insurance, generally 50 - 100% increase over your old premiums).
Now admittedly scenario #3 is fairly unlikely BUT, you need to know that it is an option for the crown. All it takes is a hard assed crown, or they feel you need to be "tuned in"..lol.
Personally, if it were me. I would say the copper cut me a pretty good break, and call it a day.
BUT only you can decide what works best for you. I would be cautious about "delaying" asking for disclosure until 6 weeks prior, as the crown may argue, and you won't know how the JP will rule, that you had months to ask and waited too long. In my experience cases outside the GTA don't experience the same level of delays etc.
Good luck