I inject at 25% but I have no intercooler on a high compression engine. Also I have not played with lower rates yet. Remember your engine uses a lot of fuel at high load, so 300L/hr is not as big a number as it seems.
I manually set the arduino PWM frequency to 122hz to run the fuel injector. Here is a link.
https://arduino-info.wikispaces.com/...-PWM-Frequency