Knocking down the fuel pressure is not the answer, you may have a 255lph pump but you're still sittin at 38-39psi, any little adjustment you make will be adjusted out by the computer by changing the pulse width on the injectors.
BTW when I rev my car I also get a little black smoke, but I know for a fact that my car is running very lean because I have the dyno sheet with the O2 reading to prove it.
Dont jack around with things before first understanding how it all works.