Does anyone know if the Sti ECU will offer any gains, and if it can be plug and played in a WRX of the same year or close?

I have a big eye, 01, and can get an ECU for an Sti.

should be plug'n play, i remember somebody did it.
but i doubt it has much improvement over stock ECU since the ECU will retard the map itself due to the knocking from 91 gas.
the boost should be set at 1.2bar (17.5psi ish) on JDM STi ECU so thats a gain.

Remember while you will gain hp and be able to get more boost your speed will be limited to 110 mph.. thats what japanese ecu's are set at by law...you need get that taken care of if you use a japanese ecu.