We've succesfully downloaded the data from GE-Power chip, and raised RPM's from 7000 to 7300. After burning the nice collection of 4 chips for us, all worked and are still working great in all cars. But I was no able to understand the tables and the motronic editor program theese few years ago so we've finished just copying data and chips.
Somewhere about february this year I've tried to look for any info about motronic editor and after spending few hours on it, I've finally found VEMS, which seems to be much better sollution for the engine. Finally I'm collecting money for the VEMS unit
In M42 all is made really that well, that combining own chip is trully not effective unless You have sport cams and ITB and exhaust with more flow. On the other hand If You have engine modded that way combining it with motronic chip is still restrictive because of AFR which doesn't let Your engine breath far more.
So for stock engine just use one of theese "+17 HP" units which are plenty on e-bay and for modded engine use something smart and programmable like Megasquirt or VEMS for example. /theese are the cheapest reasonable ECU's availlable - Some says that it is hard to setup idle with M42 on ITB's and megasquirt, so ask yourself if You need a car for the street /than go Link or Autronic or any stuff which makes kits exactly for this engine/ or if You need a car for the track /than go Haltech/ Or If You are the real enthusiast and You just like motronic - play with if :-)
Some Years ago the programmable ECU's were impossibly expensive, now we have
http://www.vems.hu so we can mod our engines really well and it doesn't really ruine our pocket :-)
This is not only mine point of view - many other tuners have found stock ECU too restrictive to be used with highly modified engine.