How about using simple math and basic physics? Why make a mountain out of a mole hill?
OK . . . Have at it !
How are you going to determine the maximum speed of the sinker, right at the moment of release ?
If you're going to try to use time of flight vs. distance, that won't be accurate, since the angle is different every time and there is no practical way to precisley measure it. Also, since the sinker does not fly perfectly straight through the air, the aerodynamic drag force is constantly changing, as the angle of attack of the sinker changes. It would also be necessary to take into account the precise air density, wind speed, and it's vector, relative to the cast, too.
All of that was already discussed in that UK article. In over 18 forum pages, no one had a definitive means to calculate it. Therefor, I am pretty certain it would have to be directly measured ( Radar gun or accelerometer ), unless you have the means to precisely measure all those variables and the mathematical forumulae to calculate it, accurately ?