I would fight it, request disclosure and go from there. You could plead guilty with an explanation and hope for a lower penalty but your insurance wont care, a ticket is a ticket and your rates will most likely go up as a result. Also, the ticket will remain on your driving record for a period of time which wont help in any subsequent stops by police. I'm not saying there isn't risk in fighting it, because there is, but this is the only route to totally get rid of the ticket.
and I second this
Originally Posted by propr'one
Remember: Demerit points dont matter unless you're losing your licence. Fines for speeding are small. You're fighting to keep your insurance cheap. Admitting guilt to an officer is NEVER the right thing to do, especially when he admitted to you he had no idea how fast you were going. (Officers cannot "guess" your speed based on how fast they were going to catch you, that will never stand up in court.)