Gains would be:
slightly worse emissions at idle
no change in power
Would require:
remap, but not just the simple stuff like the main fuel table, also the injector scale table etc, which most people mapping the standard ecu wont have access to
It would be better to just paint your current injectors really if you want that cool big injector look without actually needing bigger injectors. lol
To get more power from these engines its more airflow you need to achieve, more fuel is the easy bit but if done without more air will mean LESS power not more.