GX CS4 Compressor - Initial Impressions

I wouldn't recommend 15 psi input unless you want to prematurely wear out and break your compressor. I use 3 PSI and if I only fill to 300 bar that's no worse of a load on the motor then filling all the way to the 350 bar that is capable of.
Do you know what flow rate you get at 3 PSI? Thank you for your input.
 
I don't know the flow rate, but the output of the CS4 is a little more than stated in the manual. I measured the power used by the CS4 to set the pressure level. I set it so it is below the maximum power reached testing with the dead head plug to maximum pressure 350 bar when I fill to 300 bar.
I have a couple fittings ordered for my CS4-i. They will be here Thursday and I will try your method.