FWIW, that sounds rather optimistic. The Eta motors were a product of the fuel crisis, designed for low pumping loss (efficiency@ low rpm), high torque, good fuel economy, but are kinda 'underachievers'. as BMW 'sporting' motors go. To get the gains claimed, you'd likely also need to change the cam, induction, and exhaust (i.e. headers, cat back exh.), the chip alone won't get you there.
I put an Autothority (
www.autothority.com) chip and FlowTech (low restriction cone-type air filter) in my `87 325is, and it made a noticeable difference , but I doubt it was more than 15-18 hp. It certainly did crisp up the throttle response and improved 'driveability', but it was pretty thirsty when you hit the upper rev range with any regularity. Around town and cruising on the interstate, the mpg was pretty normal, but the 'zing' was pretty addictive, and teh honk from the FlowTech was pretty cool . . . HTH