I'm amazed you were disappointed, maybe the car wasn't fully run in, as the demo I drove didn't seem much quicker. However my car has 16.5k miles now and is sweet as a nut, JCW was added 1500 miles ago and I have to say the difference is pretty big. Not low down in the rev band but the top end is wicked now, before I would change up at 5.5k but now you can go as far as 6.5k before changing, and as for the noise!!!!
I have also done some timed runs from 50 - 70 in 3rd gear, pre JCW did 4.1 secs, which I thought was impressive, post JCW I have recorded 3.6 secs!!!!! A whole half a second quicker!!!!!!!!