Actually it's 4Kw, which is about 5 bhp - which is nearly 25% of your claimed figures, so not insignificant.
Where did you get the 4Kw error in calcs from ?
Putting aside concerns about M mode being on and M off in your biggest claimed gains, are you saying above that your before and after mid-pipe mod runs were not done straight back to back? The testing we did at Evolve was literally do some runs, change the mid-pipe, do some runs.
My answer to that is in post 59
I expect the gains to get a little bigger after some time on the road and some ECU adaptation - which I'm sure is what you're desribing with the runs getting better and better