You have proven that your reaction time is good enough to capture lightning at that speed. You can however shoot much slower, like 2 seconds or somewhere in between. Using auto ISO like you were, you'd meter just for the ambient light choosing shutter speed then adjusting the aperture. Even though the lightning is much brighter, it is short in duration (usually). An average bolt is about 1/10th of a second (I had to look that up). So with a 2 second shot, the sensor is only recording the bright light 1/20th of the time the shutter is open. The rest of that time the pixels are recording darkness which will be averaged once the photo is complete. Lightning is harder than using strobes because the amount of light reaching the camera can change in duration and intensity from each flash, affecting the exposure.