It depends upon your taxable income. The $78,750 figure is the maximum amount, for married filing jointly, that will be taxed at the 0% rate. However, any amount above that rate (including the amount that exceeds your $500,000 exclusion) is taxed at the 15% rate (until you get into the next bracket, 20%).
Your best bet would be to look at the Qualified Dividends and Capital Gain Tax Worksheet in Forms Mode.
