I have a Superchips upgrade. This is done on a franchise basis so results may vary, however the figures and graphs they publish
http://www.superchips.co.uk/ are quite conservative (~144 bhp for a CDTi).
The place I went to had a dynomometer, so they took before & after readings. (I had an ITG air filter fitted at the same time). It went from 132bhp to 153bhp, but more importantly lots more torque down to ~1300 rpm.
Two runs plus remap & filter was about £450.
It is a lot more tractable pulling top gear down to ~25mph. I didn't notice any change in fuel consumption but others have. Max toruqe up to 360 Nm @ ~2400rpm.
I explained to the insurance brokers that I wanted more tractability. The insurance went up about 10% at next renewal.
HTH,
Regards,
Kearton