Average speed calcs on 407 are trivial. Long ago the invoices showed you entry and exit times and mile markers. If they wanted to control speeding, that is the easiest road by miles. They do not want to control speeding.Turn the 407 into a pay-as-you-play speedway. BIG tolls, everyone knows. It's not being used by anyone anyway ?
Now, to your point, 407 could change the rate based on how fast you are going. Travel at the speed limit, pay the posted rate. Travel at double the posted limit, pay 4x the rate. Lots of people would happily pay and that compensates 407 for increased wear and closures for crashes caused by those with more wallet than talent.