I tend to find the hacker argument slightly compelling for a longer power down period.

One solution I've considered for this is making it so that you can only use your master password/owner key to power down fast. If a hacker has that, then your account/stake is lost anyway for however long it takes to power down. But if you use an active key for the power down, then it could be longer. I think this would protect against the possibility of someone accidentally giving out their active key and then losing their stake.