B2L2

I agree just go ask for a fine reduction.  If you have clean record in BC, use that as a point.  Use whatever reason you could think up of.

However, I don't see how "not familiar with MPH vs KPH" as a reason since you're driving ~140 and must be passing almost everyone else on the HW already.

I believe most speeders could spot the cop when they pass him.  So most will immediately slow down and cops seldomly need a long chase.  While, in your case, you don't know where the cop tagged you and where he started to follow you.  You are in a bad situation to argue.

B2L2

Tell me what you are going to do when "you got an excellent job, but that requires you to go down to US for meeting".  In my previous job, I even need to drive down to WA for meetings and work.

While you may not "like" to go to US, but things not always go along with your will.

B2L2

Well, maybe not passing everyone and I don't consider she is that outrageous (I have been doing worse).  But if I were driving 90mph in 70mph zone, I wouldn't need to look at my "meter" to know that I'm well over the speed limit.  So just using the unfamiliar meter reading as excuss is pretty lame, I consider.

B2L2

~80secs => call for the backup already?  Did you misread something?

Also, doesn't it really matter whether the siren is on or not?  You have to yield even when the emergency vehicle is flashing its lights.  It maybe an excuse to reduce the fine though, if it didn't have siren on.

Back to 20mph or 30mph over, do you actually know what's your speed at that moment?  The police probably had record on his laser gun, and they usually wrote down a smaller number already.  If you know in fact that you weren't not 30mph over, then yeah, go dispute that.  However, you never mentioned what's your traveling speed so far.