Oh, to add I now have a lovely turbo whine from the exhaust and performance has picked up. It's not massive, never was going to be but there's definitely more power and urgency low down and less restraint up top. I realise this can be a placebo so I took her to a road I know whell where I also know the character of the car like an extension of myself; results were that it bit hard and span up low down while reaching higher speed more quickly than I am used to on this particular stretch.
A very good mod on an N54