I agree completely with angeloc & hippo.
After I stopped 'playing' with the new found power I did actually get about 3mpg more.
This applied to all the other power improvements I have made.
All in all the EGR bypass, the new silicone hoses to fix leaky rubber ones, and a Synergy2 have raised the mpg to around 43 from the 36 I used to get commuting to work. It also pulls stronger from 1500 to 2000 rpm which is great for off-road.
I still have to control the urge to make full use of the performance, but meaningful economies can be made.