I had exactly the same experience-BUT-after a second drive and a few miles of varied traffic conditions I can now really feel the difference on my Mini One. Whereas before it wouldnt rev through the range-now its zings through to 5000rpm with a distict step up at 3000 revs.
It seems that the car's ECU needs to "learn" the new codes-The same experience is reported in Go Mini Magazine. Some tuning company found that it was only after a couple of journies that people really begin to feel the difference.
There is a rolling road day next Sunday which is on the pistonheads website and I am really tempted to go along to check the difference.