The 250 to 750 motor core swap will not be visible.
The 750 core how ever has now been modified in the last few months and now looks like the older cheaper Rad specialty cores that many of the earlier videos complained about. In their defense, Bafang claims that these new cores are now lighter and more efficient. Swapping my core from 500w to 750W definitely improved the power band especially in the upper ranges. Just don't make my mistake I did of using an electrical lube to better waterproof the motor connecter as that product can electrically isolate the male and female brass connecters from allowing the full voltage to the motor.
The biggest noticeable improvement though will come from the 35A controller swap...But..If a policemen knows his e bikes, there is a pretty big visible size difference between the size of a stock controller and a 35A controller upgrade.