Just like anything there is an efficiency range where the injectors with function best and that can very by brand. Everyone I spoke with in regards to Subaru injectors said that they like to function on the high side of the IDC range.

As a general rule, the lower the IDC the better you are but at the same time you don't want to go over board and end up on the other end of the spectrum.

And yes, you can tune for different cc injectors. It's not the injector itself that gets tuned it's the signal the computer send to the injector telling it when to fire and when to rest.