impedance doesn't matter? Since when? I have never heard that before.
If you get high impedance you can just run it without the resistor pack.
You can run any impedance you like if you were so inclined, you just need to set up your own resistor pack to get the correct impedance for the ECU.
Measure the actual impedance of your system in the car, and the impedance of the injectors, and setup your own resistors to get the same as stock... not that hard.
There's an acceptable range though, so you don't have to be exact. Low impedance injectors with the resistor pack, high impedance injectors without the resistor pack, and you're good to go.