If you plan to do CNP, honestly just do it right from the begining and go to a crank sensor and cam sensor setup, and get the 558-118 main harness. I wish I had done that with my 1992 GT. My Lightning is CNP.
As far as how it runs, I did a complete makeover of the driveline, so it would be hard to say, I did a fresh motor, new heads, cam, blower and the Holley HP. I think on a mild setup you probably honestly would not see much difference, but timing errors with TFI seem to be very common one you get a higher and faster revving combo.
I think the X is a nice system for those looking to upgrade from the old tech EEC-IV, but if you have a more radical combo, you might want to pony up for a HP or Dominator.