Opel uses Bosch and yes.... in many ways it's better.... mostly because people can tune the ECU where as a Daewoo ECU does not get much attention from aftermarket companies.
The C20XE has been making 150hp since the late 80's.... for it's time that was quite a bit of power.
As an example.... here is one company that does chip tuning...
http://www.v-tuning.com/n_a_tuning.htm
They can make the 2.0L 16V run at 170hp without any other significant changes to the engine other than upgrading the grade of fuel used.
There is lots of room to make these engines more powerful, even the 1.6L managed 150hp without much in the way of problems ( not by V-tuning ... done by lotus during the design of the 1.6L )
Daewoo engines run a speed density system ( Air Pressure sensor, Air Temp sensor, Throttle Plate sensor, RPM ) which calculates the fuel based upon how dense the air is ( Pressure and Temp ) along with the speed of the engine.
So most people would call it a MAP (manifold absolute pressure ) engine management system.
The Bosch system uses a MAF ( Mass air flow ) which is basically a hot wire going through the center of the intake.
The more air flow, the more it cools the wire and changes it's resistance.
So in a MAF system they are directly measuring airflow.
Each system has it's advantages and disadvantages... but what it comes down to in this case is the fact that there are dozens of companies that are out there modifying the Bosch ECU's where as there is perhaps one for the Daewoo ( someone in Korea )
Personally... it would almost be easier to go with an aftermarket standalone for your engine than to try and wire in a whole Opel engine management system.... there are lots of guys who have already done that in UK/Europe and have had great success.
The best way to gain naturally aspirated engine power is by increasing the compression and increasing the RPM.
There are kits for the 2.0L to allow you to rev to 10,000 RPM or 12,000 RPM but they are very expensive ( come from Germany ) as it requires the replacement of most of the internals and valvetrain.
Compression is easy.... one can drop in new pistons.
One can also mill down the head or have the cylinder head compression chamber shape changed.
Where labor is cheap the head work is the easiest since it does not involve buying parts.... but you need to have someone that is experienced or they may end up making less power than you started with.
