ecu alone, especially the craptastic stuff out on the market right now like the god all mighty haltech or aem will not give you the most power.
if you really want to talk about tuning a motor its not all about just injector. as much as you like to make a head that flows equally to each cylinder you really cant. you can come close to it but it will not be exact. to compensate you get engine management that can tune spark advance individual to each cylinder. you will be surprised how much it can help. for all the fan boys out there its not a big deal but when my boss use to rebuilt ferrari f40 engines, usf3 vw motors, as well as ferrari cup motors it makes a difference to make the most horsepower because that is what wins races and in the end gets you paid.
even with a plenum itb's have an advantage over a big single throttle body. pick up any book on fluid flow. its is all about velocity. volume will not help a "high performance" engine when the fluid has no inertia and doesnt fill the cylinders completely.
all racing engines that use itb's still have a plenum. it might be made out of CF but they still have it. in fact in most sanctioning bodies that have inlet size restriction thats how it is regulated.
some pics
btw this motor still had a CF plenum