How low would you go...

[locutus2002]

the ICM model does not account for position, blind or stack size. All very important in this situation.

Short stacks equity in the pot is irrelevant.
Hero has about EV 550K if he folds, $ 250K if he loses and EV 650K if he wins. (according to ICM).

Betting 300K to win 100K is a terrible bet. Short stack is all in next hand, hero should probably fold everything other than AA. The chips won are worth much less than chips lost because of the preponderance of chips held by the big stack. If you make the stacks more similar, the EV goes up substantially. In other words the match is already over (in the most likely case).