That's a fair point, a nuclear bomb is so disastrous it would be better to let one person die than a small chance the nuke will go off. However we have significantly changed the order of magnitude here, 10 million people is 1000x more than the number of tracks.

In regards to the original question: I don't think feeling responsible for 5 deaths would be 5 times worse than feeling responsible for 1 death. The emotional cost of going from 0 deaths to 1 death is much higher than the emotional cost of going from 1 death to 5 deaths. The "greater good" argument says do nothing, my ability to sleep at night says pull the lever.