depends. for a regular engine where nothing else is done than the chip, i do not believe in any claim stated by the chip manufacturer or distributor.
when an engine has additional changes like cams the chip is a must. the gain is still in question.
for diesel engines, a chip is a way of tuning that delivers improvement with the chip opnly, but that is diesel engines.
I had a chip in the car i had before the bmw and i got very disappointed as nothing, really nothing was improved. furthermore i never saw a dyno that shows what the chip really did. what you see is almost always with another exhaust system, some other sort of intake, or other kinds of changes. never ever could anyone present prove that the chip itself really delivers what it promisses. oh and btw, all chip i know require higher octane gaz. heck higher octane gaz gives more power even without a chip, so what's the deal? (i knmow it's to prevent knocking as the motronics are changed, but still it so fishy)