My X was remaped about 2 years ago incl' exhaust mods ( 3.0d ) the increase was to be exact 203Kw & 615Nm. That is a dramatic increase from standard and in my view well worth the exercise, as far as fuel economy couldn't care less the 3.0d is still so economical anyway I didn't notice decrease, after the remap the tune will adapt to your driving style ( so I was told ) if you want the full gaf POWERS1 is involved in this field. Note the increase for petrol engines (non turbo) is marginal to say the least.