As far as I'm aware, (although I'm sure GrahamL will be along soon to correct me if wrong) if you were to replace the standard chip with a GTEC 1 and still using the standard Fiat EBV, (see above posts for description EBV), then you would get approx 1.2bar boost in all gears with upto 1.4bar overboost. I also believe the GTEC1 does not adjust the ignition, it only changes the boost level on the standard EBV and has different fuel maps. Should be good for approx 30bhp. However on a standard coupe 1.2 bar will shorten the std turbo life quickly, and the standard intercooler will also struggle to cope. (In saying that I think quite a few coupe's on the forum have been running fine with this set up). You should get an engine health check done by one of the Fiat specialists, (Powerfiat, TorqueItalia, Motomech) however before fitting the chip and should also think of getting it rolling roaded to check the fueling is still ok with your particular car.
GTEC2 chip I belive has similar levels of boost if you were to use the standard fiat EBV but also runs extra ignition advance and therefore gives more power, (maybe 40bhp+). However the extra ignition it gives means you will need aditional cooling to keep the combustion temperatures down, ie Front Mounted Intercooler / water injection etc.
If you fit you own PRV/PBV/EBV then you will be able to set the boost level you want (usually somewhere between 1.0 - 1.4bar depending on which turbo you have and what intercooler/water injection). The Gtecs will then just set the fueling maps the car uses, (+ignition advance in the case of the Gtec2).
The ideal route if you are looking for more power but safely is the Unichip/custom mapped chip. This will set the optimum fueling and boost levels that your particular coupe can safely habdle.
Chris