I find that when really hitting the keys hard one doesn't usually get values over 120 so to make things easier on myself I tend to set the max value a bit lower than this.  I find something around 110-112 is a nice top value.

I also tend not to curve this line anywhere by adding other points.  Just a linear progression all the way to the top.

Which leads to the simple "curve" of:

Velocity = [0, 112; 0, 127]