My Kanger T2 is at 2.4-2.5 ohms and my Phoenix CE3s are at 2.4-2.6 ohms, on a Vision Spinner I get a burnt taste going higher than 4.2v on either. I read somewhere that you double the volts roughly based on ohm rating of carto or atty, doesn't seem accurate to me. 4.0-4.2v seems right.