I have posted a couple of message on the problems of oscillation of power as well as a metallic noise when revving my new STi8.
In case anyone ever experience the same, my dealer has now recognised the problems which was 1)a blow-off valve for the turbo causing the metallic noise.The response apparently should be quicker when this noise is apparent...

2)The oscillation was quite simply the air-con when in 6th gear can cause this slight coughs and vacilation. I am not surprised no one suggested this solution. I guess it never gets that hot in Britain so you guys remove the system which prevents this problem from occuring anyway.