The higher the voltage the higher the current through the body. Now the exact resistance of a person varies enormously, in particular if we take into account th

The higher the voltage the higher the current through the body. Now the exact resistance of a person varies enormously, in particular if we take into account things like rubber boots or if the person managed to ground herself. But as long as the system can deliver it, the current through the body will be 250 times higher when the voltage is 25000 V than when it is 100 V. Now a very low current through the heart might kill you, so with a little bit of bad luck or stupidity you'll die from a 100 V source. Like you are replacing a lightbulb in an old fixture with one wet hand resting the other one on the kitchen sink. 25000 V will almost certainly kill you. The moisture outside you rubber boots probably has low enough resistance to let a deadly current through your body. The exception is of course the static shocks. Here you are saved by the extremely low total charge. To summarize, yes it is the current that kills you, but it is the voltage that matters.