-before: NYC $5.1MM, Miami $4.2, difference $900k
-after: NYC $4.9MM, Miami $3.9, difference $1MM
So for some reason, you decided the NYC lifestyle is worth a $900k hit in your total income (which after tax is about $5MM), but $1MM will make you pack up and move to Miami. Really?
If you earn only capital gains, please note that your property tax rate in Miami is much higher. Sure, you'll be able to deduct more for federal tax purposes, but that's faint consolation as overall, you'll still end up paying more.
All in all, this is probably a submarine piece by the realtors in Miami hoping to get the rich guys in NYC to spend of few minutes even considering buying property there. It doesn't matter that the tax calculus does not make sense, maybe they'll like the sun ...