I've found some rudimentary stuff on irs.gov, but I haven't found what I wanted.
I want to know how much income is actually subject to payroll taxes versus how much is subject to income taxes. I mean overall. Wages below like $93,000 (I think) get Social Security, and there's no cap for Medicare wages, but other income (notably capital gains, dividends, and interest, which is most of what the rich make) is immune from taxes.
The point is to determine if you eliminate payroll taxes completely, how could you adjust the marginal income tax rates to bring in the same revenue? Payroll taxes suck, they're stupid. Paying "in" to Social Security and Medicare is a joke, they're social programs that benefit all of us whether we actually use them or not, so we all should pay. Eliminating regressive payroll taxes will bring about tax fairness. Also eliminating them would eliminate the employer contribution, which would be relief for small businesses. Payroll taxes are also double taxation on couples.
So if I can get this data, I can run the numbers. It's actually fairly simple, you can figure out multiple ways to adjust the brackets.