$20M, assuming I don't have to share (if I have to split the pot, $20M afterwards).
My reasoning: cash payout is about half, then I lose half to taxes. $5M left over. Put into a diversified portfolio. I should be able to pull 4% per year after that, which is $200k. Sounds like a lot, but, I might live another 40 years. Doesn't sound so hot then, so I might only pull say $100k initially, then let my standard of living go up.
At that $20M, I'm making one call to my employer--that they can mail me whatever is at my desk as I'm not coming back...
Of course, mo' money is mo' better, I wouldn't turn down a higher amount...
[Haven't played in years. But do I still dream? sure do.]