ill go out in a minute and unplug the Map sensor and see wot happens.

I suppose it could be a mis-fire...it is very consistant if it is, and is defo only evident when under load...not to sure wot the rev-limiter on these cars is like, the only way i can describe it is a very Soft Cut and it is possible for the revs to climb above it if its held on the limiter for a while i.e it kicks in at 4800rpm but if i hold it there it will climb to 5000rpm