My (now for sale) tractor constantly returned 33mpg around here after chipping. When towing the caravan to the Newent meet, it managed a disappointing 23mpg - about the same as our previous 2.0 auto!
Markseth has an un-chipped job (like my latest tractor), and his returns 33mpg locally too.
The chip that's supplied to us OOFers basically returns this engine to 'pure BMW' spec of 143BHP, (from the Vx spec of 128BHP), plus 5% - so we're looking at a tad over 150 horses.
Although I'm not convinced that there's any improvement in fuel consumption after chipping, the car certainly had superior driveability. Boost also came in lower down the revs, although with some black smoke on initial acceleration. I also experienced some 'studder' at around 1500rpm, though this seemed to cure itself.
My present '99 mini-facelift, (and Markseth's too), performs well enough, and there are no plans to chip either of them. Every '99 (or newer) that I've driven runs far better than the previously-built models, though I've yet to fathom this one out!