First, talk with a lawyer and an accountant. The at-stake amounts are large enough that's short money. Second, I'd strongly consider doing some/all of this af

First, talk with a lawyer and an accountant. The at-stake amounts are large enough that's short money. Second, I'd strongly consider doing some/all of this after Jan 1. That will put your ISO+AMT tax into 2016, which will push your tax bill on this transaction to April 2017. (It may make sense to do a smaller amount before year end, depending on your current AMT situation). (And make sure you make estimated payments (plus withholding) for 2016 that exceed 110% of your 2015 bill -- that way, you can kick the final bill all the way to April 2017). Finally, the penalty for paying late is not THAT bad: given the amount of money, it may make sense to file in April 2017, pay what you can, and work out a payment plan with the IRS. You are not the first to have this scenario happen.