You would be surprised at how much these injectors can flow, and/or how little we use them. And you brought up a cool point with dual vs single injectors.
They are awesome little pieces. There is no variable ...well, lets do better. They are an on/off switch. Either 100% open, or 100% closed. No in between.
The twin injector is used as much for where it shoots the fuel in as opposed to actually needing the amount doubled.
At 12,000 rpm, we might be at a point where its open 70% of the time.
But, as you have guessed, if its capable of keeping the engine supplied at 12,000, there would be no problem with adding 50% more fuel, at 6000, if needed.
Thats not to say a powercomamnder is an answer, anymore. Now, we need access to timing.
I'll steal this from Motocross Action with regards to dual injectors. I could not think of a simple way to say this, and they did...
(10) Mutually dependent. On a single-injector engine, the engineers must figure out an average lag time and increase the pulse width accordingly to cover all the bases. With two simultaneously operating injectors, the pickup delay can easily be covered up by the difference between fuel traveling a short distance and fuel coming from farther away. One thing is certain: dual injectors are here to stay, because they work on an engine that makes power from 5000 rpm to 13,000 rpm.