This is in no way true, but lets say the fraction is 93HP produces 112mph. So 93 * a = 112...so a = 112/93. So hp * (112/93) = 84...so using your '86 626 fraction your motor is currently making about 70HP. So if a stock Zetec is at 125 your car should be making, with the MTX, like 105HP. So using your fraction again, you should be able to go 126MPH without the speed limiter. Which is pretty damn close to how fast a Zetec will go.
So you can very roughly approximate your car now at around 70HP.
