To answer the OP, top marginal rates start to become counterproductive and produce negative side effects if they go much over 50%. I don't really see a need for punitive taxation, so a 50% combined top marginal rate is about as high as I would go.
Would you favor say a top marginal rate (and this is for all taxes combined, not just federal), that goes a bit higher than 50%, say to 55%, until such time as the 50% number is hit based on all taxable income (and that means with all schedule A deductions phased out), rather than just the top marginal rate? I don't have a problem with a guy earning 2 million, paying half of that amount in total taxes (federal, state and local). But I would not want to go higher than that. This metric does not represent that much of a tax increase on very high income earners than the present regime, at least for those who don't game the system playing hard the deduction game, e.g. taking deductions for charitable contributions of highly appreciated art works, where they escape paying capital gains on such art, while taking a deduction for its full fair market value. Also the pension deductions should be cut back for such high income earners.
